Eels constantly cause fascination within aquarists but many true eels, Anguilliformes are simply too large for the majority of aquarists. A much smaller but fascinating alternative comes from Cypriniformes, a relatively medium sized genus known as Pangio. I’ve previously owned Pangio for many years and they are one fish I would definitely keep again.
Pangio myersi and Pangio semicincta/kuhlii
Pangio contains around 32 species (Bohlen et al., 2011), exclusive to South East Asia. They are clearly small anguilliform (the eel shape, not the taxa) but borderline very similar to the larger loach relative, Misgurnus anguillicaudatus (weather loach). For the aquarist the taxonomy can prove confusing with revisions that are not always well known such as the synonymy of Pangio semicincta and Pangio kuhlii (Kottelat, M & Lim, 1993) but is frequently debated seemingly with little explanation as to why (Eschmeyer, 2025). Molecular phylogenetics hasn’t seemed to have solved the confusion, or it’s suggested that the two species are the same (Bohlen et al., 2011). Another problem is Pangio myersi is nested within the two (Bohlen et al., 2011) although easily diagnosed for aquarists by thick barring from dorsal to abdomen (Kottelat, M & Lim, 1993).
There doesn’t seem to be immediately much morphological diversity in this genus, there is a diversity of patterning. While many will attempt diagnosing species by colouration, this has been called into question with solid marked individuals being identified as those with stripes (Bohlen et al., 2011). Like all loaches they contain small scales that to some can make them seem scaleless.
My interest is largely in morphology and like many there seems to be no anatomical studies. The majority focuses in the taxonomic records and this makes it really difficult to understand the morphology that might have ecological importance and also husbandry. We can clearly see a inferior (ventrally facing) mouth so they feed below and given the barbels it seems a common trait with those rooting in the substrate given they are not mobile.
Pangio cuneovergata
In the aquarium hobby we keep very few species but a diversity is starting to be imported and not just as bycatch. You can expect to find of the distinctively patterned species Pangio semicincta/kuhlii, P. myersi and P. shelfordii. The smallest species that is now being imported in reasonable numbers is Pangio cuneovergata. There are a few solid coloured species and these are likely Pangio oblonga and P. anguillaris, potentially also P. malayana who is shown to have solid individuals.
Pangio semincincta/kuhlii
How to Identify your Pangio?
This is a tricky topic but there are multiple sources that holds clues.
Figure 1: A Key to the Pangio of the Malay Penninsula as described in: Bohlen, J., Šlechtová, V., Tan, H. H., & Britz, R. (2011). Phylogeny of the southeast Asian freshwater fish genus Pangio (Cypriniformes; Cobitidae). Molecular Phylogenetics and Evolution, 61(3), 854-865.
As described previously there are some hints you can get from experiencing the species in captivity but there is a lot of cross referencing, where you can linking to a locality and exploration of images that could be of use. I find Bohlen et al. (2011; Fig 1) possibly the most useful of the papers for identification of species even if images are limited. One must also remember where you might have imported from one country it doesn’t mean that is where it is caught.
Habitat
There is little ecological details on these fishes. Habitat likely differs per species. Largely found in blackwater although potentially also highly turbid waters with variable or seasonal currents (Bohlen et al., 2011). Yet in the literature very little else is recorded.
Figure 2: Geographical distribution of Pangio according to INaturalist (2025)
Some assumptions can be made from the locality of these fishes (Fig 2), particularly in reference to temperature, although you will also need to check against elevation and other factors such as is the water body sheltered and therefore cooler. INaturalist (https://www.inaturalist.org/)and GBIF (https://www.gbif.org/) can be useful here although neither make any records of environmental factors. If someone is familiar with these websites then there is other extractions of data that can be done but I am not someone who works with species distributions. Other parameters can be tricky without knowing the geology of the region, some rocks dissolve more readily whereas others allow tannins or just rainwater to drain rapidly through without dissolving minerals.
We also know Pangio almost always seem to breed in tanks with gravel, there are probably exceptions so the substrates must have gravel where they are located with the exception of maybe more elongate species who similar to lamprey bury in silt and sands.
What setup would suit Pangio?
Generally I don’t think the current ideal setup for Pangio needs any adapting, sandy areas and gravel based areas, leaf litter providing many hiding places but also wood or rocks for more solid refuges.
One of my setups in 2017 for multiple Pangio spp., filtered by a Fluval 306 (I think).
A reasonable current but it wouldn’t have to be that strong so a sponge filter would suffice. I would consider with externals, internals or similar filters whether the fishes could get in, they are notorious for finding their ways into filters so either providing an inlet guard or changing filtration method particularly for those like Pangio cuneovergata. Undergravel filters sound great and somewhat are, the fishes will make their way into them and likely also live below the grids but many do report them spawning well there.
There is no doubt these fishes come from more soft acidic water based on locality and therefore I recommend a pH of around 6-7.5 for various reasons. There is flexibility and these fishes have proven themselves very hardy in captivity. Total Dissolved Solids (TDS) below 200ppm but ideally below that 100ppm range unless your water has potentially skewed values. Temperature is definitely the tricky one without knowing exactly the temperature of their caught locality, I would personally cross reference where they are found with water temperatures of the area and who knows other species in the area might have ecological data. Generally 24-28c seems the most ideal but you could be flexible particularly on that upper end to go higher.
They are often noted as being particularly shy although I’ve found with dimmer and dappled lighting but also frequent exposure they don’t seem to be that shy and show a lot of normal feeding and explorative behaviour. Plenty of cover gives them somewhere to retreat to.
References:
Bohlen, J., Šlechtová, V., Tan, H. H., & Britz, R. (2011). Phylogeny of the southeast Asian freshwater fish genus Pangio (Cypriniformes; Cobitidae). Molecular Phylogenetics and Evolution, 61(3), 854-865.
Kottelat, M & Lim, K. K. P. (1993) A review of the eel-loaches of the genus Pangio (Teleostei:Coditidae) from the Malay Peninsula, with descriptions of six new species. Raffles of Zoology, 41(2): 203-249.
With a whole section designated to Loricariidae, I haven’t actually done a beginners guide to the group. This website largely isn’t designed for beginners but Loricariid’s are some of the most misunderstood group of fishes.
These two common names have no certain definitions, the majority of their use is a pick and mix that varies between the user. It is even more confusing that some loaches are referred to as pleco’s. All common names are equally as valid as each other. I find it easier to refer to the whole of Loricariidae as plecos, why? Figure 1 explains this situation. By excluding the subfamily Loricariinae (whiptail catfishes), you exclude Loricariichthys of which Plecostomus was synonymized with. If you exclude Hypoptopominae (Otocinclus and relatives) then Neoplecostomini and Neoplecostomus are excluded. Ancistrus, commonly known as bristlenose’s places right in the middle of Hypostominae, traditional plecos but Ancistrus also includes the medusa pleco, Ancistrus ranunculus. Then outside of all of these groups is Rhinelepinae, so that includes the pineapple pleco’s, and on it’s own Pseudancistrus genisetiger, so none of those are plecos then?
What would solve the common name issue? Simply not using them. Sadly with Loricariids you can’t avoid scientific names as many species do lack common names or share them.
Figure 1: Annotated phylogeny of Loricariidae from Roxo, F. F., Ochoa, L. E., Sabaj, M. H., Lujan, N. K., Covain, R., Silva, G. S., … & Oliveira, C. (2019). Phylogenomic reappraisal of the Neotropical catfish family Loricariidae (Teleostei: Siluriformes) using ultraconserved elements. Molecular phylogenetics and evolution, 135, 148-165.
What is the L number system?
The L number system is actually quite simple, it is a hobby made system originating from the German Magazine, DATZ. It simply designates an L number to a variant or species. It is commonly stated that undescribed species are given L numbers, this is partially true but there are many species who were described decades or over 100 years before given their L number such as the sailfin/common/leopard pleco, Pterygoplichthys gibbiceps who was described by Kner in 1854.
I am not entirely convinced the L number system is easy to use, the order of the numbers doesn’t infer anything regarding the fishes care or lineages. Multiple species can share an L number e.g. Baryancistrus demantoides and Hemiancistrus subvirdis are both L200 also known as green phantoms. Hemiancistrus subvirdis is likely the same species as L128 although that is a topic for another day. One species can have multiple L numbers, which don’t always describe populations or all of the morphological variation of the species e.g. Baryancistrus xanthellus has 4 L numbers.
To top it off there are fake L numbers, L600 for example described Pseudacanthicus leopardus who already has the L numbers, L114 and L427. The L number system is only up to around 530 species so far. The letters added to L numbers aren’t a part of the L number system and increase confusion. Sometimes species are given by the hobby the L number of an entirely different species such as L144 which doesn’t even exist in the hobby and hasn’t done for decades or L056 for Parancistrus aurantiacus when actually that L number refers to an undescribed brown Pseudancistrus.
There is additionally the LDA number system which does overlap slightly but isn’t so expansive.
Introduction
Loricariidae, pleco’s are the largest family within the order of fishes known as Siluriforme also known as catfishes or welse, representing 1050 currently described species (Fricke et al., 2024). This group is exclusive to South and Central American freshwaters although has invasive populations in many continents.
Panaque nirolineatus from Maidenhead Aquatics at Ascot.
The family is identified by a downwards (ventrally) facing oral disc shaped mouth, in some species this is more of a suction cup whereas others they cannot attach to surfaces well or at all. This trait isn’t exclusive to Loricariids but it is not quite the same in other groups. Further more, Loricariids are defined by having a body covered in bony scutes, more scientifically known as dermal plating, not scales as catfishes lack scales.
Baryancistrus chrysolomus.
Not does Loricariidae just have dermal plating but they have spines known as odontodes, external teeth (Fig 2). Sometimes these are sexually dimorphic but not always, they can also be shed seasonally.
Figure 2: Odontodes found on I believe Peckoltia sabaji.
Loricariids realistically are one of the most morphologically diverse clades of fishes.
This diversity means that as a group, Loricariids are really difficult if impossible to generalize, research is paramount for this group.
The size of plecos
As one of the most diverse groups of fishes their size varies vastly, 0.2-0.8cm in Parotocinclus halbothi (Lehmann et al., 2014) to 100cm SL possibly in Acanthicus adonis. There is a wide diversity of sizes within many groups so there is no shortage of smaller and larger species. At the end of the article I will recommend reliable websites, there is frequent misleading information about the adult size of many species.
It is important to recognize reliable websites will use standard length, from the head to the base of the caudal/tail fin. That caudal/tail fin will be excluded as these can vary in length. I mention this as many people will not consider this measurement and forget their fish grows much bigger then they would originally consider. This is explained in detail in this article.
There are a few myths regarding Loricariid diets I will summerise:
Pleco’s are largely carnivores, there are plenty of papers discussing their diets and while I wont cite them all Lujan et al. (2015) summerises it well.
Pleco’s become carnivorous with age, there isn’t any studies regarding change in diet as the fishes age. Unlike most fishes, the majority of Loricariids break down their food before it enters their mouth, so the size of the fish doesn’t limit their food item, so not gape limited. This means unlike many other fishes their food item doesn’t need to change with size.
Pleco’s clean a tank, while the majority are algivores and detritivores (Lujan et al., 2015) there is a wide diversity in niche partitioning (Lujan et al., 2011) and therefore those algivore’s specialize in certain algae’s. These algae’s seem not to be those that are an issue in the aquarium. Given their lifespan and waste production, they could be an expensive solution to high nutrients.
Pleco’s don’t eat cyanobacteria, they actually don’t just eat those that are pests in the aquarium, in the wild they feed on cyanobacteria (Valencia & Zamudio ,2007).
Always check the ingredients as some diets that claim to contain algae’s might contain anything from none to 5%.
In simple NO, they do not need wood. The only species that utilize wood are in the genera Panaque, Panaqolus, Hypostomus cochliodon group, Pseudoqolus and perhaps Lasiancistrus heteracanthicus. These groups all share unique spoon shaped teeth they can gouge into wood and if found among wood, wood is found in their gut (Lujan et al., 2017). No other Loricariid has wood in their gut, I’ve scoured gut records but they simply don’t have the jaws or teeth to gouge into wood. There have been many studies to confirm these fishes do not eat/digest the wood (Watts et al., 2021; German, 2009), instead they are just evolved to feed on biofilms, like other species from where other species cannot access, within wood (Lujan et al., 2011).
Peckoltia compta
What parameters do pleco’s need?
While the general idea is that Loricariids and in general anything South America requires soft, low conductivity and acidic water there is a wide diversity of parameters. Some species are found in lower temperatures while other much higher, 28c or higher (Collins et al., 2015; Urbano‐Bonilla & Ballen et al., 2021). Other misconceptions are that South American habitats have a lot of leaf litter and is black water, this is completely untrue, there are many different habitat types (Bogotá-Gregory et al., 2020). In general the majority of Loricariidae are rheophilic and would benefit from a current within the aquarium although there is some diversity (Krings et al., 2023). In general any current within the aquarium is a lot weaker then any of the weaker streams in their wild range.
Planet Catfish has really accessible information to identify parameters before looking into the scientific literature.
What decor do plecos require?
This is largely the only consistent aspect of Loricariids. If anyone has kept Loricariids they will know how much they like cracks, crevices, hiding spaces, rocks, branches and in general cover. There are many caves and tunnels on the market designed for the preferences of a variety of species. I recommend stacking up wood or rocks in a careful way so nothing falls but this will create many more caves.
Tankmates
This will always be based on experience and understanding of the fishes. It’s important to recognize a few key things about Loricariids.
Loricariids do not often feed rapidly but even if they do it can take them minutes to an hour to reach food. Fast feeding fishes such as most cichlids, loaches, tetra, livebearers and goldfish particularly in large numbers are a bad idea.
Their temperature might not overlap.
They will need a current, some more then others which this means they wont work with fishes like long finned Betta splendens.
While some Loricariids feed on food items that they wouldn’t naturally it doesn’t mean it is good for them. Bloat can happen in some genera more then others. So I do not recommend keeping other fishes with Loricariids who you plan on feeding anything like beefheart.
Hardness, conductivity etc. We don’t actually know the KH or GH of the water many of these fishes come from, usually we have conductivity and pH records for many waters. Ideally these fishes are ill-suited regardless with Rift Valley cichlids, generally the biggest issue is above, those cichlids feed way too rapidly for any Loricariid.
Collins, R. A., Ribeiro, E. D., Machado, V. N., Hrbek, T., & Farias, I. P. (2015). A preliminary inventory of the catfishes of the lower Rio Nhamundá, Brazil (Ostariophysi, Siluriformes). Biodiversity Data Journal, (3).
Bogotá-Gregory, J. D., Lima, F. C., Correa, S. B., Silva-Oliveira, C., Jenkins, D. G., Ribeiro, F. R., … & Crampton, W. G. (2020). Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages. Scientific Reports, 10(1), 15349.
German, D. P. (2009). Inside the guts of wood-eating catfishes: can they digest wood?. Journal of Comparative Physiology B, 179, 1011-1023.
Krings, W., Konn-Vetterlein, D., Hausdorf, B., & Gorb, S. N. (2023). Holding in the stream: convergent evolution of suckermouth structures in Loricariidae (Siluriformes). Frontiers in Zoology, 20(1), 37.
Lehmann, P. A., Lazzarotto, H., & Reis, R. E. (2014). Parotocinclus halbothi, a new species of small armored catfish (Loricariidae: Hypoptopomatinae), from the Trombetas and Marowijne River basins, in Brazil and Suriname. Neotropical Ichthyology, 12, 27-33.
Lujan, N. K., Cramer, C. A., Covain, R., Fisch-Muller, S., & López-Fernández, H. (2017). Multilocus molecular phylogeny of the ornamental wood-eating catfishes (Siluriformes, Loricariidae, Panaqolus and Panaque) reveals undescribed diversity and parapatric clades. Molecular phylogenetics and evolution, 109, 321-336.
Lujan, N. K., German, D. P., & Winemiller, K. O. (2011). Do wood‐grazing fishes partition their niche?: morphological and isotopic evidence for trophic segregation in Neotropical Loricariidae. Functional Ecology, 25(6), 1327-1338.
Lujan, N. K., Winemiller, K. O., & Armbruster, J. W. (2012). Trophic diversity in the evolution and community assembly of loricariid catfishes. BMC Evolutionary Biology, 12, 1-13.
Roxo, F. F., Ochoa, L. E., Sabaj, M. H., Lujan, N. K., Covain, R., Silva, G. S., … & Oliveira, C. (2019). Phylogenomic reappraisal of the Neotropical catfish family Loricariidae (Teleostei: Siluriformes) using ultraconserved elements. Molecular phylogenetics and evolution, 135, 148-165.
Urbano‐Bonilla, A., & Ballen, G. A. (2021). A new species of Chaetostoma (Siluriformes: Loricariidae) from the Orinoco basin with comments on Amazonian species of the genus in Colombia. Journal of Fish Biology, 98(4), 1091-1104.
Valencia, César Román, and Héctor Zamudio. 2007. Dieta y reproducción de Lasiancistrus caucanus (Pisces: Loricariidae) en la cuenca del río La Vieja, Alto Cauca, Colombia. Revista del Museo Argentino de Ciencias Naturales nueva serie 9(2): 95-101.
Watts, J. E., McDonald, R. C., & Schreier, H. J. (2021). Wood degradation by Panaque nigrolineatus, a neotropical catfish: diversity and activity of gastrointestinal tract lignocellulolytic and nitrogen fixing communities. In Advances in Botanical Research (Vol. 99, pp. 209-238). Academic Press.
Inkbirds are a brand/product of external thermostat, these are units that regulate the temperature change provided by a heating unit. Without a thermostat the heater will not switch off at the desired temperature. Many heaters contain their own ones but very frequently they do malfunction, so in theory these external units are more reliable. Some heaters do not have an internal thermostat such as many titanium ones so would require an external thermostat.
There isn’t much of a range in external thermostats with either Inkbird or D-D around. The reptile hobby does have a wider range of thermostats but it is unclear how much and if they are waterproof unlike these two aquarium brands.
Generally the majority of people set their external thermostats as the only thermostat with the heater unit itself at a much higher temperature. Personally I prefer to use both as a fail safe, so the heaters are only setup just above that of the Inkbird and therefore if the Inkbirds fail hopefully those thermostats of the heaters should cut it off.
The other benefit is these are connected to WIFI and therefore can be controlled from my phone. On top of that it will send push alerts for any issues and if I notice that the units are disconnected it could hint to a powercut.
These thermostats do not require only to be controlled via your phone but also can be used manually if that is preferred. It also means they will stay running during any WIFI outage. The temperature history also allows for you to loosely track how long it takes to heat the tank and also if and when there was any power outages.
Review/opinion:
I have two Inkbird’s myself and have done since 2021, they have proven reliable to me and a necessary part of my aquariums since having heaters fail in the past. They are really good units, setting them up can be a challenge but certainly worth it. Where I do keep fishes that require 28c I think it puts a lot of pressure on most heaters so the inkbirds really help here. The thermostat allows for two heaters to be attached meaning it doesn’t take as long to reach the desired temperature.
Setting up your Inkbird
Step 1: Download the Inkbird app on the Apple App store or what is required for Android.
Step 2: Your home screen should look similar to this without any inkbirds setup. Click on the Plus Icon.
Step 2: Choose the product you have, here the Inkbird-306A.
Step 3: Choose the mode. I find AP mode the easiest, it might not be automatically set to that so press the other mode option to select it.
Step 4: Press the WIFI button on the Inkbird until the light on the unit blinks slowly. This might take several goes.
Step 5: The Inkbird will then require your WIFI including password of which needs filling in.
Step 6: It will request for you to join the network that is provided by the Inkbird unit. Go onto your WIFI settings and join that network.
Step 7: Press connect.
Step 8: It will then connect which can take time, keep the phone close to the Inkbird unit while connecting.
Step 9: All connected, you can name the unit.
Running Inkbirds
This is the main screen, it has several updates so hadn’t always looked like this. It should be pretty self explanatory how to use.
The central value is the temperature where it will tell you if the heaters are providing heat or not. This screen is also where any warnings will appear such as low temperature, wide temperature range between probes etc.
You can select temperature by pressing on that range T1-T2.
Under settings you will find this screen, this is where you can select alarms. I have mine quite extreme as during water changes it can be a real pain if you set it to 2-4 degrees under. Heating time might also be worth considering, it’ll produce an alarm if too long so consider how long after a water change the aquarium takes to reach it’s desired temperature.
The majority of discussions regarding lighting in the aquarium is very plant centric, plants depend on light to a much higher degree then animals. Although the extent that aquarists looking at plant growth goes to maybe verges on the unnatural, probably because many aquarium plants we keep are not naturally aquatic so some are evolved for much higher degrees of lighting.
Fishes having eyes and melanin so do respond to and can see light (Guthrie, 1986). Previously in an article focusing on UVB and lighting intensity I discuss the importance for enhancing colouration particularly and any benefits of UVB. In this article I want to talk more in a broader sense of the importance for lighting itself rather then to go into depth on aspects of the lighting spectrum.
One of the largest debates in animal biology regarding vision is how much can they see, fishes is a large category and even in freshwater there will be a massive diversity in colour vision. Some fishes also do not have any eyes, usually due to a trilobite lifestyle in caves, only the Mexican cave fish, Astyanax mexicanus seems to really enter the aquarium trade with any frequency and some of these have reduced eyes known as microphthalmia (Borowsky, 2018). Unlike many other vertebrates fishes display other senses (Gill, 2018) that allow many to cope without eyes as some fishkeepers might have noticed after their fish had lost one or both.
What colour should my lights be?
Generally it would be considered the most natural light would be white light and this is partially true, it has the widest range of colours in it after all. One thing to consider if we are replicating a fishes habitat and wanting to give them lighting that will benefit them is the influence of depth. The deeper the water the more certain colours are filtered out such as reds. I personally think that unless you are using the brightest colouration for an aim it probably has no benefit to the fishes, personally I much prefer those warmer tones. We do know at least in humans the actual colours of the spectrum exposed to the eye does effect the physiology so I personally think this means that white light is so important.
Many freshwater fishes are tetrachromatic, having four colour cone receptors in the eye rather then the three of typical humans or two-three of reef fishes (Marshall et al., 2019). This colour vision does depend on the light intensity, so at lower intensities freshwater fishes tend to be trichromatic (Neumeyer & Arnold, 1989). So this does pose an issue where people use blue lights to watch particularly catfishes at night, if the fishes can see that blue light it is likely disrupting them. I personally would only recommend doing this for short periods so the fish can rest. It might also be a factor that if using only blue lights the lighting is dimmer anyway which is why they are more active rather then them thinking it’s night. Personally I’d rather use a camera for hidden behaviour.
How long should lights be on? If at all?
Fishes much like humans have an internal clock known as a Circadian rhythm, this can be influenced by multiple factors but in particular light (Vera et al., 2023). This means having a regular cycle where the lights are on and off is beneficial. This is not just limited by eyes, even without eyes certain physiology can occur meaning a fish can identify day and night (Frøland Steindal & Whitmore, 2019). This means a regular schedule of day and night is important for fishes much like with people, changes seasonally would work.
There is no doubt a range in nocturnal and and diurnal fishes that we keep, probably many are also crepuscular. The length of time required to sleep likely also varies between individuals and species, some taking short frequent rest periods and much longer periods (Reebs et al., 1992). Sleep is incredibly important for fishes, so it is a necessity to provide that time for them (Leung et al., 2019).
References:
Borowsky, R. (2018). Cavefishes. Current Biology, 28(2), R60-R64.
Frøland Steindal, I. A., & Whitmore, D. (2019). Circadian clocks in fish—what have we learned so far?. Biology, 8(1), 17.
Gill, A. B. (2019). The sensory ecology of fishes. Journal of Fish Biology, 95(1), 3-4.
Guthrie, D. M. (1986). Role of vision in fish behaviour. In The behaviour of Teleost fishes (pp. 75-113). Boston, MA: Springer US.
Leung, L. C., Wang, G. X., Madelaine, R., Skariah, G., Kawakami, K., Deisseroth, K., … & Mourrain, P. (2019). Neural signatures of sleep in zebrafish. Nature, 571(7764), 198-204.
Marshall, N. J., Cortesi, F., de Busserolles, F., Siebeck, U. E., & Cheney, K. L. (2019). Colours and colour vision in reef fishes: Past, present and future research directions. Journal of Fish Biology, 95(1), 5-38.
Neumeyer, C., & Arnold, K. (1989). Tetrachromatic color vision in the goldfish becomes trichromatic under white adaptation light of moderate intensity. Vision research, 29(12), 1719-1727.
Reebs, S. (1992). Sleep, inactivity and circadian rhythms in fish. In Rhythms in fishes (pp. 127-135). Boston, MA: Springer US.
Vera, L. M., de Alba, G., Santos, S., Szewczyk, T. M., Mackenzie, S. A., Sánchez-Vázquez, F. J., & Planellas, S. R. (2023). Circadian rhythm of preferred temperature in fish: Behavioural thermoregulation linked to daily photocycles in zebrafish and Nile tilapia. Journal of Thermal Biology, 113, 103544.
Many fishes display lumps, spots and bumps which can happen due to a range of pathological conditions whether it being pathogens or other factors. These can easily be confused and if concerned or confused please consult a fish pathologist or trained fish specialist veterinarian. This page is only to help give some clarity
All sources here are from scientific papers and many of the images from these papers for a reliable diagnosis unless otherwise stated for clarity purposes.
Microscopy is required in many cases for a confirmed diagnosis and therefore I recommend their use. Some stores might have one available to be used. In other cases more advanced diagnostic techniques might be required and provided by a pathologist via a veterinarian.
Protozoan ciliate pathogen which can cause large mortalities in later stages.
Ichthyophthirius multifiliis on a Rift Valley cichlid, Aulonocara sp.? Image obtained from: Thomas Kaczmarczyk (www.djpalme.de.vu) on Wikipedia.
Occurrence: Seems to be very common and in my opinion largely occurs when fish are sufficiently stressed.
Diagnostics: White spots on the body of the fish, can also be accompanied by shedding of the slime coat. The spots can be varied in size and number. This ciliate additionally targets the gills where it causes the most stress on the fish (Yang et al., 2023; Mallik et al., 2013). This spotted appearance is commonly confused with Epistylis which if symptomatic (of which mostly it is not) appears more as a plaque so will not appear in this article (ESHA video; Ksepka et al., 2021; Valladao et al., 2015; Wang et al., 2017, Wu et al., 2021). Both pathogens can appear with Aeoromonas bacteria that additionally causes hemorrhaging (Kumar et al., 2022).
Microscopic image:
Ichthyophthirius multifiliis under the microscope, images obtained from Yang et al (2023). Yang, H., Tu, X., Xiao, J., Hu, J., & Gu, Z. (2023). Investigations on white spot disease reveal high genetic diversity of the fish parasite, Ichthyophthirius multifiliis (Fouquet, 1876) in China. Aquaculture, 562, 738804.
Treatment: The most frequent treatments provided in the aquarium hobby is malachite green with either formalin, formaldehyde or copper. Obviously copper is often a concern for those with invertebrates in the aquarium. Salt the old age treatment can work and as a study ABDULLAH-AL MAMUN et al. (2021) infers it depends on time of treatment. There seems to be a multitude of papers narrowing down the best treatment and to me this infers maybe there is no real answer, there might be increasing immunity of the ciliate or just this species is so diverse. Generally it’s assumed the best method is to avoid introducing any fish showing symptoms or on the same system with those who do. Copper sulphate additionally has been shown to treat white spot (Schlenk et al., 1998). In a later 2008 study formalin did not have any effect on the ciliate whereas copper treated it within 14 days (Rowland et al., 2008) which is around two rounds of treatment by most bottles. I therefore just looking at these three studies would not recommend formalin and maybe therefor formaldehyde for treatment and instead focus on copper and maybe salt needs further examination.
Velvet (Oodinium, Piscinoodinium and other dinospores) and related taxa
One of the most unusual parasites of fishes being an algae known as dinoflagellates.
Piscinoodinium pillulare outbreaks: piscinootest. Ciência Rural, 48. on the gills of a fish (Gomes et al., 2018). Gomes, A. L. S., Costa, J. I. D., Benetton, M. L. F. D. N., Bernardino, G., & Belem-Costa, A. (2018). A fast and practical method for initial diagnosis of Piscinoodinium pillulare outbreaks: piscinootest. Ciência Rural, 48.Piscinoodinium spp. infections (Esmail et al., 2015). Image obtained from: Esmail, M. Y., Astrofsky, K. M., Lawrence, C., & Serluca, F. C. (2015). The biology and management of the zebrafish. In Laboratory animal medicine (pp. 1015-1062). Academic Press.
Occurrence: Reasonably common, I can’t comment on cause. It seems Oodinium seems to be less common then Piscinoodinium.
Diagnostics: Different from white spot, being algaes they tend to have some coloration to them. Usually appears as small golden spots across the body, the fish are often lethargic. Mortality is not particularly rapid (Levy et al., 2007). It is not always obvious beyond hemorrhaging (Sudhagar et al., 2022).
Microscopic image: Not entirely required and diverse, although can make it easier to compare.
Piscinoodinium sp. copied from Sudhagar et al. (2022). Sudhagar, A., Sundar Raj, N., Mohandas, S. P., Serin, S., Sibi, K. K., Sanil, N. K., & Raja Swaminathan, T. (2022). Outbreak of Parasitic Dinoflagellate Piscinoodinium sp. Infection in an Endangered Fish from India: Arulius Barb (Dawkinsia arulius). Pathogens, 11(11), 1350.
Treatment: Treatment rarely seems discussed. As these are photosynthetic I agree with many aquarists that keeping the lights off for even two weeks will not harm the fish and even if it minorly effects the algae that’s better then nothing. The aquarium hobby largely jumps to copper based treatments along with malachite green mixed in with methylene blue, it doesn’t seem the most resistant pathogen and I wonder additionally if a fishes immune system handles some of it. Copper is suggested to work (Lieke et al., 2020). There seems to be no research on methylene blue other then being an anti-protozoan compound. Similarly with malachite green, no treatments even salt have any strong background to their effectiveness. The other issue is these compounds can effect the microbes within the aquarium (Yang et al., 2021). All I can say is I had success with the NT labs anti-parasite treatment containing copper sulphate and formaldehyde along with switching the lights off.
Dermocystidium
The strangest in appearance of pathogens, much like a worm but far from that, their taxonomic placement is unclear but they don’t move.
Dermocystidium on a hatchet fish, Gasteropelecus.
Occurrence: Reasonably frequent with a diversity of fishes soon after obtaining.
Diagnostics: Worm like in a variety of forms and size, can be encapsulated by pectoral fins or around the body. Some might appear singularly other fishes might have a lot more. These do not move like nematodes but are extremely diverse (Fujimoto, et al., 2018; Persson et al., 2022).
Microscope image: Not required.
Treatment: It is largely agreed in the aquarium trade which I agree that these protozoans as unsightly as they are do disappear with time and handled by the fishes own immune system.
Worm cysts
Not really possible to obtain much scientific research on the topic with the time I have free. But it does happen and seems frequent with wild imports.
Occurrence: Not common at all, seems to arrive with import.
Diagnostics: Looks much like white spot but larger cysts. Stubborn and white spot treatments do not work regardless of the fish showing no lethargy or poor health.
Microscope image: Usually distinctively different from white spot velvet by size and shape.
Treatment: As suggested by the name, wormers tend to work. I cannot remember which I used but likely first praziquantel, levamisole and flubendazole might work as well.
Tumors
If a tumor occurs certainly this is a situation where veterinarians are recommended.
Occurrences: There are many caused within fishes, sometimes it is genetic causes such as in the dragon scale of Betta splendens, viral causes (Coffee et al., 2013) or dietary (Žák et al., 2022). On a quick scan of the literature papilloma viruses are not associated with tumors.
Diagnosis: These can be large growths, they can be vascularized supplied by blood vessels. Unlike viral growths on my observations tend to be rounder and do not appear in many numbers.
Microscopy: Not required.
Treatment: Discuss with a specialist fish veterinarian.
Viral papilloma and herpes viruses
These are commonly mistaken for lymphocystis and can be very complex growths. Technically Papilloma refers to epithelial groups but can display similarly to herpes viruses. In the aquarium trade it doesn’t seem clear which we are handling and regardless treatment is the same. A wide range of herpes viruses are associated with fishes from KHV, carp pox (Davison et al., 2013) and channel catfish herpesvirus (Davison et al., 1992).
Viral papilloma’s likely caused by a Papillomavirus (PV) in a Pterygoplichthys pardalis, image sourced from Reddit, poster: Render et al., 1721.
Occurrence: Seems reasonably common right now. This virus I can assume once contracted is not removed from the fishes body but are suppressed by the immune system. Koi Herpes Virus (KHV) is fatal and while not wildly common any suspected occurrence might require contacting environmental authorities.
Diagnosis: These are round or very tuberous numerous growths, much more like warts while symptomatic but asymptomatic individuals and time might not display any symptoms (Tarján et al., 2022; Rahmati-Holasoo et al., 2015). Very understudied when it comes to aquarium fishes so whether we are dealing with a herpes or traditional papilloma virus is difficult to say. Rahmati-Holasoo et al. (2015) infers that most viral growths we are seeing in Loricariids is caused by a Papillomavirus, although a previous study by Hedrick et al., (1996) in carp inferred similar growths and concluded due to a herpes virus.
Treatment: Time, these viruses cannot be cured only prevention of introduction. Very few are fatal. These viruses are generally specific to closely related fishes so transfer should not be an issue.
There is a wide range of unknown growths in fishes we can only make assumptions, veterinary professionals and vets would be worth consulting. I have seen a number which didn’t conform with any of these.
References:
ABDULLAH-AL MAMUN, M. D., NASREN, S., RATHORE, S. S., & RAHMAN, M. M. (2021). Mass infection of Ichthyophthirius multifiliis in two ornamental fish and their control measures. Annals of Biology, (2), 209-214.
Coffee, L. L., Casey, J. W., & Bowser, P. R. (2013). Pathology of tumors in fish associated with retroviruses: a review. Veterinary Pathology, 50(3), 390-403.
Davison, A. J. (1992). Channel catfish virus: a new type of herpesvirus. Virology, 186(1), 9-14.
Davison, A. J., Kurobe, T., Gatherer, D., Cunningham, C., Korf, I., Fukuda, H., … & Waltzek, T. B. (2013). Comparative genomics of carp herpesviruses. Journal of Virology, 87(5), 2908-2922.
Esmail, M. Y., Astrofsky, K. M., Lawrence, C., & Serluca, F. C. (2015). The biology and management of the zebrafish. In Laboratory animal medicine (pp. 1015-1062). Academic Press.
Fujimoto, R. Y., Couto, M. V. S., Sousa, N. C., Diniz, D. G., Diniz, J. A. P., Madi, R. R., … & Eiras, J. C. (2018). Dermocystidium sp. infection in farmed hybrid fish Colossoma macropomum× Piaractus brachypomus in Brazil. Journal of Fish Diseases, 41(3), 565-568.
Gomes, A. L. S., Costa, J. I. D., Benetton, M. L. F. D. N., Bernardino, G., & Belem-Costa, A. (2018). A fast and practical method for initial diagnosis of Piscinoodinium pillulare outbreaks: piscinootest. Ciência Rural, 48.
Hedrick, R. P., Groff, J. M., Okihiro, M. S., & McDowell, T. S. (1990). Herpesviruses detected in papillomatous skin growths of koi carp (Cyprinus carpio). Journal of Wildlife Diseases, 26(4), 578-581.
Ksepka, S. P., & Bullard, S. A. (2021). Morphology, phylogenetics and pathology of “red sore disease”(coinfection by Epistylis cf. wuhanensis and Aeromonas hydrophila) on sportfishes from reservoirs in the South‐Eastern United States. Journal of Fish Diseases, 44(5), 541-551.
Kumar, V., Das, B. K., Swain, H. S., Chowdhury, H., Roy, S., Bera, A. K., … & Behera, B. K. (2022). Outbreak of Ichthyophthirius multifiliis associated with Aeromonas hydrophila in Pangasianodon hypophthalmus: The role of turmeric oil in enhancing immunity and inducing resistance against co-infection. Frontiers in immunology, 13, 956478.
Levy, M. G., Litaker, R. W., Goldstein, R. J., Dykstra, M. J., Vandersea, M. W., & Noga, E. J. (2007). Piscinoodinium, a fish-ectoparasitic dinoflagellate, is a member of the class Dinophyceae, subclass Gymnodiniphycidae: convergent evolution with Amyloodinium. Journal of Parasitology, 93(5), 1006-1015.
Lieke, T., Meinelt, T., Hoseinifar, S. H., Pan, B., Straus, D. L., & Steinberg, C. E. (2020). Sustainable aquaculture requires environmental‐friendly treatment strategies for fish diseases. Reviews in Aquaculture, 12(2), 943-965.
Mallik, S. K., Shahi, N., Das, P., Pandey, N. N., Haldar, R. S., Kumar, B. S., & Chandra, S. (2015). Occurrence of Ichthyophthirius multifiliis (White spot) infection in snow trout, Schizothorax richardsonii (Gray) and its treatment trial in control condition. Indian Journal of Animal Research, 49(2), 227-230.
Persson, B. D., Aspán, A., Bass, D., & Axén, C. (2022). A case study of Dermotheca gasterostei (= Dermocystidium gasterostei, Elkan) isolated from three-spined stickleback (Gasterosteus aculeatus) captured in lake Vättern, Sweden. Bulletin of the European Association of Fish Pathologists.
Rahmati-Holasoo, H., Shokrpoor, S., Mousavi, H. E., & Ardeshiri, M. (2015). Concurrence of inverted-papilloma and papilloma in a gold spot pleco (Pterygoplichthys joselimaianus Weber, 1991). Journal of Applied Ichthyology, 31(3), 533-535.
Rowland, S. J., Mifsud, C., Nixon, M., Read, P., & Landos, M. (2008). Use of formalin and copper to control ichthyophthiriosis in the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell). Aquaculture research, 40(1), 44-54.
Schlenk, D., Gollon, J. L., & Griffin, B. R. (1998). Efficacy of copper sulfate for the treatment of ichthyophthiriasis in channel catfish. Journal of Aquatic Animal Health, 10(4), 390-396.
Sudhagar, A., Sundar Raj, N., Mohandas, S. P., Serin, S., Sibi, K. K., Sanil, N. K., & Raja Swaminathan, T. (2022). Outbreak of Parasitic Dinoflagellate Piscinoodinium sp. Infection in an Endangered Fish from India: Arulius Barb (Dawkinsia arulius). Pathogens, 11(11), 1350.
Tarján, Z. L., Doszpoly, A., Eszterbauer, E., & Benkő, M. (2022). Partial genetic characterisation of a novel alloherpesvirus detected by PCR in a farmed wels catfish (Silurus glanis). Acta Veterinaria Hungarica, 70(4), 321-327.
Valladao, G. M. R., Levy-Pereira, N., Viadanna, P. H. D. O., Gallani, S. U., Farias, T. H. V., & Pilarski, F. (2015). Haematology and histopathology of Nile tilapia parasitised by Epistylis sp., an emerging pathogen in South America. Bulletin of the European Association of Fish Pathologists, 35(1), 14-20.
Yang, C. W., Chang, Y. T., Hsieh, C. Y., & Chang, B. V. (2021). Effects of malachite green on the microbiomes of milkfish culture ponds. Water, 13(4), 411.
Yang, H., Tu, X., Xiao, J., Hu, J., & Gu, Z. (2023). Investigations on white spot disease reveal high genetic diversity of the fish parasite, Ichthyophthirius multifiliis (Fouquet, 1876) in China. Aquaculture, 562, 738804.
Wang, Z., Zhou, T., Guo, Q., & Gu, Z. (2017). Description of a new freshwater ciliate Epistylis wuhanensis n. sp.(Ciliophora, Peritrichia) from China, with a focus on phylogenetic relationships within family Epistylididae. Journal of Eukaryotic Microbiology, 64(3), 394-406.
Wu, T., Li, Y., Zhang, T., Hou, J., Mu, C., Warren, A., & Lu, B. (2021). Morphology and molecular phylogeny of three Epistylis species found in freshwater habitats in China, including the description of E. foissneri n. sp.(Ciliophora, Peritrichia). European Journal of Protistology, 78, 125767.
Žák, J., Roy, K., Dyková, I., Mráz, J., & Reichard, M. (2022). Starter feed for carnivorous species as a practical replacement of bloodworms for a vertebrate model organism in ageing, the turquoise killifish Nothobranchius furzeri. Journal of Fish Biology, 100(4), 894-908.
Like any other organism fishes can host pathogens and contract diseases, unlike many other pet related hobbies we are dealing with a wide diversity of different species. The diseases of aquarium fishes is there for a vast topic.
As my specialty is in the evolutionary biology of fishes, diseases are not my specialty. That is not to say like any other fish biologist I do not encounter them, given I am often not using high magnifications I actually am more familiar with larger ectoparasites then bacteria or protozoa. I do have a background in taxonomy as well so am familiar with understanding how even these bacteria, protozoa, fungi etc. are diagnosed to a degree.
Previously there have been many brilliant aquarium books focused on disease and I think more then anything I recommend an aquarist to have at least one. These books were often written by those with a background in pathology, included images of microscope slides and based in science.
Books I’d recommend (there will be others I have forgotten):
Discus Health, TFH Publication by Dieter Untergasser
Handbook of Fish Diseases, TFH Publication by Dieter Untergasser.
The Interpet Manual of Fish Health: Everything You Need to Know About Aquarium Fish, Their Environment and Disease Prevention, Firefly Books Ltd by Dr. Chris Andrews, Adrian Excell and Dr Neville Carrington.
The Practical Guide to Fish Diseases by Dr. Gerald Bassleer
The main issue with disease is to take anything also marketing a product with a pinch of salt unless it’s discussing a general compound e.g. malachite green, formaldehyde etc.
Diseases of aquarium fishes has become one of the most hotly contested topics within the aquarium hobby of recent years. With many websites making unfounded claims that lack citations where maybe they should to backup any novel ideas or information. This makes diagnosing disease for the general fishkeeper rather challenging. I hope I can make it a little easier or give areas to start researching.
This topic will cover multiple articles and therefore this contents should help guide a user through this page and others.
One of the biggest factors when it comes to any organism of preventing disease is ensuring the organism is healthy. There are several influences that might mean a fish is stressed enough to become more susceptible to disease; behavioral, environmental and also diet. If an organism is stressed then the immune system might not be functioning as well as it could and will be less able to fend of disease, this isn’t something new. Some disease might additionally be directly caused by these factors rather then by external pathogens.
So, lets explore preventative care.
Preventing disease by understanding specific fish behavior.
This is probably the most difficult to identify and sometimes the most difficult to cater for as we know so little about fish behavior. Here there are probably two outcomes of not catering for a fishes behavior; poor physiological health or abnormal behavior.
Poor physiological health is very obvious, a fish might have tattered fins, lost scales and reduced colouration. It could be that the fish is being directly attacked in territorial aggression or from a more predatory tankmate. In some fishes just simply removing an offending individual might solve the issue but with some fishes such as the Aulonocara (peacock cichlids), mbuna (multiple genera), Haplochromis etc. of the Rift valley this can create instability in the social hierarchy of the group (Piefke et al., 2021). Of course removing some worst offending species would maybe be a benefit and therefore considering what species are to be included to start off. These voids in hierarchy can create more aggression as individuals are additionally are then identifying where they all fit. It’s a common assumption to assume aggression is male focused, as I discuss in a previous article females do frequently display aggression (Female Aggression).
Aggression can just be simply territorial, Neolamprologous cichlids can be good examples of this where individuals will maintain a space and the location based often on maintaining resources reproductive, predator protection and dietary. Fish sociality can be so very complex so it’s not entirely simple (Walter et al., 1994). This territoriality can also be seen in many Loricariids (Plecos) but also Anabantoids such as Channa or gourami’s, not always related to reproduction but just defense of a space.
Even many shoaling species might show aggression and therefore in that context a good number with an appropriate sex ratio would be best. Sociality in many species is important though, even if it is fleeting there is a behavioral enrichment, this isn’t always possible. But for shoaling and schooling species having others of the same species or population is important.
Many popular fishes can be counted as some what shoaling or schooling such as clown loaches, Chromobotia macracanthus to neon tetra, Paracheirodon innesi. These fishes alone or even in small numbers such as 3 or 6 depending on the species you might see abnormal behavior. Sometimes difficult to identify as some species are just illusive. A shoaling species kept alone could be illusive, swim erratically around the glass or even maybe shoaling with a different species. It’s definitely very context dependent. Sociality is important for behavioral and maybe even physiological development (Riley et al., 2018), we know that though from other verebtrates……. The understanding of species can be difficult but realistically multiple individuals of different species would not make up a shoal. Whether it be Corydoras or tetra, these species might not be closely related but even if they are it doesn’t mean they can communicate and therefore benefit socially. In other fishes such as discus communication is so much in their coloration given they can recognize individuals (Satoh et al., 2016), many varieties have lost or altered this ability and could result in communication issues between domestics, wilds and certain varieties. This means it’s highly likely discus can identify the different species and even populations. I have experienced this myself. Just by the fact so many fishes of the same genus or group are located together behavior likely results in this speciation.
Tankmates themselves can provide another kind of harm, they could be eaten and vice versa. Generally avoiding tankmates that will fit in the mouth is a good rule of measure. Some fishes can expand their mouth further then expected and while many are gape limited (limited by the size of their mouth) others this limitation is minor. Even the slowest fish are more then capable of eating faster fishes, discus feeding on cardinal/neon tetra is commonly accounted and goldfish frequently feed on smaller tankmates. The biggest risk here is if the smaller fish is too big to be swallowed down and that larger fish chokes.
Goldfish, Carassius aureatus choking on an Otocinclus sp. the catfish had been housed with the goldfish for 2 years before this situation. Photo used with permission from the owner and the Facebook group: Goldfish Care.
The effect of the environment on fish disease.
More then often we think of the environment as purely about water parameters in fishes but the actual décor is important as well. I have been a long standing admin of goldfish groups and frequently seen where they have choked on gravel for example.
This is so diverse as so much can effect a fishes health.
Water parameters
The influence of water parameters on the health of fishes is so complex and so diverse, here I wont discuss hardness I have discussed it partially in the article on pH and hardness (here). Associated with mismanagement of hardness is gas bubble disease of which would require it’s own article or discussion, it is likely confused with a pH crash due to how quickly it occurs.
So, the main parameters we will focus on will be those related to nitrogen; ammonia, nitrites and nitrates. The values which cause death will vary depending on the fish and other parameters, many effects might seem asymptomatic unless a dissection is undertaken so do not assume because you cannot see an effect the fish isn’t affected. Ammonia itself burns the gills (Liu et al., 2021) but largely targets the the brain (Ip & Chew et al., 2010). Nitrite is the most well known as crossing into the blood combining with the blood to form methaemoglobin resulting in less oxygen carried around the body (Ciji & Akhtar, 2020), it can kill particularly rapidly seeming like a crash. These all are managed by a stable and cycled aquarium. Nitrate is maybe the least understood and the least studied as most studies focus on fishes with particular adaptability. This compound functions the same way as nitrites by combining with the blood to reduce oxygen saturation within the blood at higher volumes (Camargo et al., 2005). Many websites and a number of Youtubers focus on whether it kills but it shouldn’t be about rapid deaths rather long term effects, this is likely due to promoting methods where high nitrates are inevitable (Hrubec et al., 1996). So the question about low volumes becomes difficult, this is because most studies are short term and on fishes completely different from what we keep but even Hrubec et al. (1996) displays the toxicity of nitrate. It is better to assume toxicity then not just for the sake of water changes and half an hour or few hours a week, after all no one would argue for mammals to be left in their own waste because of intensive farming methods that do so.
Most of these nitrogen based compounds effect how oxygen is taken up whether it’s from burning the gills or the binding to the blood. So increasing oxygenation will not be harmful, methylene blue in small volumes is associated with increasing oxygen saturation in humans although it is difficult to find any research into the topic. Olufayo and Yusuf (2016) suggested that volumes of 67ppm to 199ppm of methylene blue didn’t increase oxygen saturation but previous research lists methylene blue as decreasing the solubility of oxygen (Khan et al., 2022). One aspect could be that largely when used in medicine it’s in humans and direct in the body, for fishes it’s added into the water so I think there is a whole other level of things at play. Another aspect of treating any higher values of these compounds is the use of Seachem prime, yes it does but decrease oxygen saturation so there is a balance (Seachem’s website).
Substrate
One of the things that least comes to mind when it comes to the health of fishes is substrates, there is so much diversity of them in stores and this can be overwhelming. Some might interact with the water parameters which is not usually ideal for many fishes as the focus of these is on plants.
The biggest risk substrate is gravels with any fish that might dig around in the substrate. It is frequently accounted particularly with goldfish where the gravel becomes stuck in either the oral or pharyngeal jaws of the fish.
Some of many situations where goldfish have choked on goldfish, used with permission of the owners and the facebook group: Goldfish Care.
Just as seriously from gravel is impaction although I have never encountered a certain case myself, if that gravel enters the digestive tract it wont exit easily unlike sand of which many fishes pass through their gut even in larger amounts harmlessly (Lujan et al., 2012).
Substrates offer an enrichment for so many fishes which is very important to recognise as so many species naturally search for food. I would rarely have a tank without it. The safest and most natural for many species is sands. One of these fishes that benefits so much are Corydoras and a number of loaches. Sharp substrates in these fishes is associated with erosion of the barbels present around the mouth although there is no studies on the topic and it is sometimes associated with the bacteria that gravel traps. This erosion leaves open wounds and an area highly open to infection.
Corydoras sterbai with erosion of the barbels caused by the sharp gravel and substrate. Image sourced from Aquarium Coop Forum, CARE and the user BMBSAD.
décor
This is probably the most logical but in the stress of setting up a tank it can be a bit overwhelming to decide what to get. Generally consider if you are having any secretive fishes they will need plenty of spaces to hide in a variety of shapes and sizes, being exposed can be stressful for them and you’ll see the stress patterning on them. When it comes to these fishes always be sure there isn’t decor that the fish can get stuck on, this seems more of an issue with artificial décor then natural.
Sharp décor can also cause wounds whether it be the metal rods in silk plants or sharp dragon rock, for many fishes this is no issue but for clumsy species or some bottom dwellers accidents happen. Some species which might have very rough spawning or aggressive behaviour then they can bash against décor so maybe avoiding anything too rough here but we shouldn’t exchange enrichment to almost bubble wrap our fishes.
Some items might have a risk if eaten, I am not sure how true this is but some people do record rasping fishes such as Loricariids feeding on the paint of some artificial décor. This is probably best avoided just because of the potential chemicals. Similar any decor from plastics you are not familiar with and might degrade in the water releasing microplastics or other compounds.
Conclusion
Obviously for preventative care there is so much more that needs to be considered. Think about the habitats these fishes experience in the wild. Observe your fishes and their behaviour, sometimes it’s worth doing so from a distance so they aren’t expecting food either that or a camera to see them at night. Some behaviour is not always seen.
What are pathogens?
Pathogens are organisms that cause disease. These in fishes can be as followed:
Viruses: Debatable if they are alive and therefore an organism. These cannot therefore do not have any treatment against them beyond keeping the immune system at it’s best and preventative care. Some viruses cannot be ‘cured’ and will always exist within the fish and some the fishes immune system will kill. Some viruses are fatal to the fish and others are not.
Bacteria: This is a massive group of organisms. Unlike viruses and like all the other groups I will later list not all are pathogens or parasites, many have different roles. These can be killed by a variety of treatments and by the fishes immune system.
Protozoa: This is a paraphyletic group of random organisms, not all are parasitic and some can be particularly difficult to treat while others much easier. A huge diversity of organisms.
Annelid/worms: Very few are ever seen in the aquarium other then leeches, these are true worms and more tricky to treat.
Nematodes: Similar to worms but not closely related at all. These are most often known for inhabiting the digestive tract or tissues in cysts. Many different wormers target this group.
Copepods, isopods: Easier to see in most situations and best removed by hand if spotted, these larger Arthropod invertebrates can be difficult to treat once becoming an infestation. The only ones a fishkeeper will usually encounter is fish lice, Argulus sp.
Algaes: The least obvious group to be parasitic/pathogenic but many are, velvet (Oodinium spp.) and related species with similar symptoms are reasonably common. This includes Cyanobacteria which are still algaes (Yanong et al., 2002). Technically as quite a lot of algae’s are protozoan and similar treatments sometimes work.
Disease and pathogen specificity.
Diseases and pathogens can be specific to certain groups of fishes or sometimes certain age demographics. A great example is some herpes type viruses many of which are specific to certain species or families (Hanson et al., 2011). This does mean if one fish has such a virus it wont be contracted by other taxa. You will also not find any confirmed cases of some diseases/pathogens in some fishes e.g. lymphocystis in carp and catfishes.
This is likely due to a diversity of different physiology between species, genera and even further families and more. Biology in general can differ so much certain groups might prevent access to certain taxa or they might lack the target organs and tissues.
Some individuals might be asymptomatic to certain diseases and pathogens.
Notes on Antibiotics
Antibiotic resistance is listed as one of the largest threats to humanity by the World Health Organisation, CDC etc. Bacteria and other pathogens are capable of resistance to a treatment on frequent exposure but bacteria being the most threatening. This has lead to many countries restricting their use, in countries like the UK they are only legal via prescription. Antibiotics unrestricted are commonly used without considering if the pathogen is actually a bacteria, if it is not it’ll have no effect but likely result in resistance of any bacteria around that are not currently a pathogen resulting in disease. In the aquarium there are many other treatments to try first. Antibiotics are reasonably specific to certain bacteria so would require knowing which are being targeted. If antibiotics are required then visit your vet, there are many fish vets within the UK who can be consulted on their opinion of the pathogen and course of treatment.
Pathogens of fishes and relevant articles to aid in diagnosis:
Discolouration and change in skin/scale condition (Unfinished)
Abnormal external bodies (Unfinished)
References
Camargo, J. A., Alonso, A., & Salamanca, A. (2005). Nitrate toxicity to aquatic animals: a review with new data for freshwater invertebrates. Chemosphere, 58(9), 1255-1267.
Ciji, A., & Akhtar, M. S. (2020). Nitrite implications and its management strategies in aquaculture: A review. Reviews in Aquaculture, 12(2), 878-908.
Hanson, L., Dishon, A., & Kotler, M. (2011). Herpesviruses that infect fish. Viruses, 3(11), 2160-2191.
Hrubec, T. C., Smith, S. A., & Robertson, J. L. (1996). Nitrate toxicity: a potential problem of recirculating systems. Aquacultural Engineering Society Proceedings II: Successes and Failures in Commercial Recirculating Aquaculture. Northeast Regional Agricultural Engineering Service Cooperative Extension, Ithaca, NY.
Ip, Y. K., & Chew, S. F. (2010). Ammonia production, excretion, toxicity, and defense in fish: a review. Frontiers in physiology, 1, 134.
Khan, I., Saeed, K., Zekker, I., Zhang, B., Hendi, A. H., Ahmad, A., … & Khan, I. (2022). Review on methylene blue: Its properties, uses, toxicity and
Liu, M. J., Guo, H. Y., Liu, B., Zhu, K. C., Guo, L., Liu, B. S., … & Zhang, D. C. (2021). Gill oxidative damage caused by acute ammonia stress was reduced through the HIF-1α/NF-κb signaling pathway in golden pompano (Trachinotus ovatus). Ecotoxicology and Environmental Safety, 222, 112504.photodegradation. Water, 14(2), 242.
Lujan, N. K., Winemiller, K. O., & Armbruster, J. W. (2012). Trophic diversity in the evolution and community assembly of loricariid catfishes. BMC Evolutionary Biology, 12(1), 1-13.
Olufayo, M. O., & Yusuf, H. O. (2016). Toxicity of methylene blue on nile tilapia (Oreochromis Niloticus) juveniles. IOSR Journal of Environmental Science, Toxicology and Food Technology, 10, 9-16.
Piefke, T. J., Bonnell, T. R., DeOliveira, G. M., Border, S. E., & Dijkstra, P. D. (2021). Social network stability is impacted by removing a dominant male in replicate dominance hierarchies of a cichlid fish. Animal Behaviour, 175, 7-20.
Riley, R. J., Roe, T., Gillie, E. R., Boogert, N. J., & Manica, A. (2018). The development of social interactions in Corydoras aeneus larvae. bioRxiv, 455188.
Satoh, S., Tanaka, H., & Kohda, M. (2016). Facial recognition in a discus fish (Cichlidae): experimental approach using digital models. PloS one, 11(5), e0154543.
Walter, B., & Trillmich, F. (1994). Female aggression and male peace-keeping in a cichlid fish harem: conflict between and within the sexes in Lamprologus ocellatus. Behavioral Ecology and Sociobiology, 34, 105-112.
Yanong, R. P., Francis-Floyd, R., Curtis, E., Klinger, R. E., Cichra, M. F., & Berzins, I. K. (2002). Algal dermatitis in cichlids. Journal of the American Veterinary Medical Association, 220(9), 1353-1358.
This has to be one of the most hotly contested, almost every brand has their own product and if someone isn’t aligned with a brand they might have their own personal reputation weighing on their method. It’s worse when it comes to fish in or fishless cycling and that might be a whole other debate.
As a long term fishkeeper who’ve had fishes for a long time I’ve not needed to cycle a tank for a long time. I have plenty of media to cycle an aquarium and I go on a precaution of not enough for the fish I’m adding so I feed less and water change more to start with. For people reading this they are likely not new to fishkeeping so probably in the same field but maybe it means we are rusty on what to recommend? I actually ask is there a wrong and a right? I don’t think so.
When thinking about nitrification and realistically microbial colonies as it’s not just archaea and bacteria (Klotz et al., 2022). So commonly we might think of these as units and because we cannot see them we do not identify them for what they are, biological organisms and effected by the abiotic conditions and the other biological organisms around them. It is a whole ecosystem where they have to compete for particularly space and oxygen. Each nitrifying organism will have it’s own range of tolerance depending on strain and species but there will be much more generalist strains and species. When it comes to what bacterium and archaea are best for our aquariums might be known but so few products label what they contain.
The flaws of research
There is peer reviewed research into the topic (Scagnelli et al., 2023) and comparing brands but it is important to recognise particularly that the effects here are largely dependent on the actual methods. Are their study aquariums representative of what we keep as fishkeepers?
Satanoperca sp. possibly S. leucostictus
It is clear from the results that many of the bottled treatments did not differ from the control where they have no effect on ammonia concentration. Tetra’s bottled bacterial treatment has statistically significant results, decreasing the levels of ammonia over 14 days by 0.562 (+-0.08). This does mean that it still stands that these products vary (Scagnelli et al., 2023). Being scientific though and in the discussion of this topic it is worth critically analysing. The test kits were not mentioned and therefore the accuracy and reliability could be of question both regarding why the other products might not be displaying statistically significant results. It doesn’t seem to be mentioned the age of the products and how close to expiry they are.
It would not be fair to include unreliable experiments that lack peer reviewing.
Dr Tim’s One and Only
One of the most interesting brands, this is a scientist who has a good background in understanding nitrification as a microbiologist and a bibliography in the field. He is an aquarist as well which is of real value to the hobby, I feel in the UK his products have been a little forgotten.
There have been no reliable experiments or investigations into his products which makes them difficult to actually evaluate. While Dr. Hovanec has extensive experience in the field and his own products I guess the issue with him doing research that can get peer reviewed into his own products is conflict of interests. His research into the world of nitrification is particularly interesting.
Few brands as it is not required by law (as far as I know?) are likely to declare what strains and bacteria they contain to avoid competition. Burrell et al., (2001) suggested Nitrosomonas marina-like as a major contributor to nitrification while, Nitrosospira tenuis-like and Nitrosomonas europaea-like bacterium contribute to the mature aquarium. This paper was also contributed to by Dr Hovanec but Dr Tims as a brand was only started in 2007 and it’d make logical sense that the products would contain these strains. It’s not to say other brands do not contain these strains as the research is open access and it likely is that many do. In an earlier paper Nitrospira moscoviensis and Nitrospira marina were further confirmed to be contributors to nitrification but later studies on that mature aquarium were not conducted (Hovanec et al., 1998).
Of course this means brands are likely containing the right strains if did properly but concentrations would vary.
Krobia xinegunesis with Corydoras granti and Cleithracara maronii
So can they live that long?
One of the largest arguments is that the bacteria are all dead, this is quite weak as we know bacteria can go into hibernation for long periods of time when conditions are not ideal, not just when they are cold. Nitrifying bacterium are no exception and can survive long periods of time sealed (Alleman & Preston, 1991). Oxygen is a known cause for dormancy and therefore preventing death (Murphy et al., 2016), this assumes they are sealed without or very limited access to oxygen and many brands are able to provide this. Another aspect is when in the presence of other bacterium if they are not in this state it’s not difficult to see how they could be outcompeted or not survive.
Conclusion
Definitely not the longest discussion as it’s so personal. My personal criticism is there is no way someone can say x fish equals requiring x amount of product, it also depends what the fish is fed on.
I didn’t want to focus on any brands really as a criticism as it would be unfair given how little we know about them. While I do want to do personal experiments on the topic it would only be so reliable, the number of aquariums I’d need and to counter for so many variables.
It’s such a controversial topic and on top of that is social media. I personally think we should be open minded but critical about brands claiming to provide something while claiming other brands do not. That includes personal brands such as social media.
At the end of the day I feel cycle an aquarium how you want, there are too many knowns the discussion of fishless vs fish in entirely cannot be settled so that is another discussion. It’s very emotive as a topic. As a fish biologist I am not a microbiologist and therefore I think it’s worth making that clear.
References:
Alleman, J. E., & Preston, K. (1991). Behavior and physiology of nitrifying bacteria. In Proceedings of the second annual conference on commercial aquaculture, CES (Vol. 240, pp. 1-13).
Burrell, P. C., Phalen, C. M., & Hovanec, T. A. (2001). Identification of bacteria responsible for ammonia oxidation in freshwater aquaria. Applied and Environmental Microbiology, 67(12), 5791-5800.
Hovanec, T. A., Taylor, L. T., Blakis, A., & Delong, E. F. (1998). Nitrospira-like bacteria associated with nitrite oxidation in freshwater aquaria. Applied and environmental microbiology, 64(1), 258-264.
Klotz, F., Kitzinger, K., Ngugi, D. K., Büsing, P., Littmann, S., Kuypers, M. M., … & Pester, M. (2022). Quantification of archaea-driven freshwater nitrification from single cell to ecosystem levels. The ISME Journal, 16(6), 1647-1656.
Murphy, C., Rajabzadeh, A. R., Weber, K. P., Nivala, J., Wallace, S. D., & Cooper, D. J. (2016). Nitrification cessation and recovery in an aerated saturated vertical subsurface flow treatment wetland: Field studies and microscale biofilm modeling. Bioresource technology, 209, 125-132.
Scagnelli, A. M., Javier, S., Mitchell, M., & Acierno, M. (2023). Efficacy of quick-start nitrifying products in controlled fresh-water aquaria. Journal of Exotic Pet Medicine, 44, 22-26.
Stendker blue turquoise discus, Symphysodon sp. x. at Maidenhead Aquatics, Ascot 2019.
Hybridisation is such a trigger word these days with many opinions for and against. First there are two definitions required:
Hybridisation: Interbreeding between two members of different species (Adah et al., 2013).
Crossbreeding: Interbreeding between two members of the same species, they might be the same variety/breed/cultivar or different.
These two terms are often used interchangeably even if they do not refer to the same event. Although these terms are different they do rely on the definition of species, genera and higher taxa which is hotly debated. One frequent definition being the biological species definition which relies on hybridisation being a barrier although is largely unreliable (Mallet, 2001).
Hybridisation as an event is not uncommon (Scribner et al., 2000), the event (or events) has resulted in the development of new species, a process known as speciation (Litsios & Salamin, 2014). Not all of the offspring might be fertile, many people in the aquarium trade might be familiar with the hybrid parrot cichlids (Amphilophus citrinellus x. Heros efasciatus), this may be the biggest barrier to speciation.
Synodontis sp. at Maidenhead Aquatics, Ascot 2019.
Barriers to Hybridisation
There are many barriers to hybridisation which really can effect the result if there is some compatibility.
Chromosomal number is the most well known barrier to hybridisation, chromosomes are units within the nucleus that contains all the DNA. Most humans have 22 pairs, fruit flies, Drosophila melanogaster have 4 pairs and the duckbilled platyplus has 26 (a lot of sex chromosomes though!), chromosomal number does not infer complexity at all and nor does the size of a genome. Generally different species might have a different number of chromosomes, this is very well displayed in the Loricariid (pleco) genus, Ancistrus (bristlenoses) which displays a diversity of different chromosomal numbers across a 50 or more species large grouping (Santos da Silva et al., 2022). During reproduction parental chromosome numbers ideally need to match to put simply. While this is a barrier it has resulted in infertile offspring, or in the example of the livebearers from Poecilidae a number of unusual adaptations. These hybrid Poecilidae have the ability to reproduce via gynogensis, asexual reproduction with the requirement of a male to stimulate the process, he contributes nothing to the offspring (Schultz, 1969) and this is displayed potentially in many species originating from hybridisation (Turner, 1980). The limitations of chromosomes really vary though but are definitely present.
Morphology is one of the obvious but so easily forgotten, organisms have to be morphologically compatible not just for the initial act but additionally for fertilisation and gestation. It might not seem it but that minor differences in morphology make a difference, what might seem obscure such as the shape of spermatozoa can differ resulting in the cell not being able to imbed into the egg, it’s even so diverse that the morphology of this cell can infer groups (Quagio-Grassiotto et al., 2020). Species often judge each other via their morphology and therefore there is some level of sameness particularly in the wild.
Behaviour, different species or even different populations might display very different behaviours. Behaviour itself is so integral to reproduction and mate choice, outside of captivity this is such a strong barrier.
Geography is maybe the most well known barrier and often can result in the other divisions. This can be within a small space such as fishes which inhabit deeper water whereas others the shallows. Barriers don’t always have to be spatial but they can also be temporal.
Golden dwarf cockatoo cichlid, Apistogramma cacatuoides
The issues with hybridisation
Hybridisation itself is not negative it’s just a force, in terms of conservation it can provide a variety of effects. Hybridisation can lead to the decline in a population of a species, most well known in the case of the Scottish wildcat (Felis silvestris silvestris) and the sister species, the domestic cat (Felis catus). As hybrids display what is known as a hybrid vigour (a mixture of traits between the two pariental species) it can change how these individuals interact with their environment and the genetic diversity of a species (Selz & Seehausen, 2019). The ecological impact of the introduction of hybrids can be described as unpredictable (Mandeville et al., 2022) which makes it difficult to identify those exact issues. Although, this argument is similar to introducing individuals who are selectively bred who might also influence the gene pool of wild individuals. It is generally not ideal, hybridisation in conservation is reserved for restoring species where no other alternative can be found e.g. Prezewalski’s horse (Equus ferus prezewalskii) and the domestic horse (Equus ferus caballus) in an effort to save the subspecies, although hybridisation is a risk to the subspecies (King, 2005).
But here we are talking about captivity, it’s highly unlikely any of our fishes will be involved in any real conservation effort or practices.
The main issue in captivity with these hybrids is so many do not go recorded, likely due to misidentifications of the parent species and lack of record keeping. Take Ancistrus dolichopterus, this species is generally diagnosed as having 8-9 soft dorsal rays, only one small individual was spotted excluding brown spots on the abdomen. While no seams were mentioned (Kner, 1854) it is commonly stated they display these, as with many other Ancistrus these often do fade with time and I have been shown individuals from the type locality lacking these seams. There are many spotted Ancistrus and over time localities and important information on them are lost. It’s more then often that these seams are how the judgement is based on what species it is. The point I am getting to is how well do we know these species and how they are defined? We are relying here on hybridisation not being able to occur but it likely does because species are kept together who are not the same species but assumed the same. I generally would assume unless wild caught for morphologically indistinctive Ancistrus, they should probably be assumed hybrids. I have frequently seen even Ancistrus ranunculus, a morphologically distinctive Ancistrus be misidentified so it’s a difficult situation. This doesn’t include how little we know about some genera, the frequency of bycatch and misidentifications from suppliers as well.
Surely those who argue against hybridisation should also argue against crossing those from different localities or populations. This is also changing the genetic landscape of a population and asks the question of how to define a species.
In captivity it does effect if you are getting what you think you are getting but for many this might not be an issue. One of the biggest worries though is because hybrids are a pick and mix of the parental species morphology and behaviour is largely unknown, it could be more similar to one parent then the other, an intermediate or totally different. Where parental species have different requirements this is also an issue.
For wild caught fishes maybe getting fishes from the same source and checking locality matches if you are not completely confident on the identification. Keep records of who is being crossed with who.
It’s quite simple to keep those who could maybe hybridised apart, this is difficult to judge as it is not just about genera but if it looks similar don’t keep them together. If hybridisation occurs clearly record that and any offspring should be sold labelled as such, if possible to pet only homes with no worries of breeding where that label can be forgotten over generations.
For captive bred individuals the situation is difficult, if you aren’t sure and they aren’t from a responsible or reliable source then don’t buy unless you plan on just having the animals as a pet, assuming you don’t want to increase the number of hybrids.
Much of the dislike towards hybrids is focused on certain species although hybrids are much more common then they seem. Fishes such as domestic discus (Symphysodon spp.) are a mixture of the three different species and definitely the different localities depending on the variety (Ng et al., 2021). Some domestic species might have hybrid origins such as the common bristlenose, Ancistrus sp. but we do not know. These species do not seem to have health related defects from their morphology although those such as the parrot cichlid, Amphilophus sp. x. Vieja sp. (not to be confused with the true parrot cichlid, Hoplarchus psittacus), clearly does have health related deformities as a result of selective breeding and hybridisation as displayed in this link to a Monster FishKeepers discussion forum.
The true parrot cichlid, Hoplarchus psittacus at Pier Aquatics, 2021
Conclusion
Hybridisation will always occur in the hobby, it is best that it is labelled so future keepers are aware of what their fishes are. If you are not completely sure of the species you are keeping then don’t breed it, ideally anyone who can identify the species should be able to cite a reliable website or the description of the species. Undescribed species might not have this so should have more precautions made such as keeping to one locality and morphology.
References
Adah, P. M., Onyia, L. U., & Obande, R. A. (2013). Fish hybridization in some catfishes: A review.
King, S. R. (2005). Extinct in the Wild to Endangered: the history of Przewalski’s horse (Equus ferus przewalskii) and its future conservation. Mongolian Journal of Biological Sciences, 3(2), 37-41.
Kner, R. (1854). Die Hypostomiden: Zweite Hauptgruppe der Familie der Panzerfische.(Loricata vel Goniodontes) (Vol. 1). KK Hof-und Staatsdruckerei.
Litsios, G., & Salamin, N. (2014). Hybridisation and diversification in the adaptive radiation of clownfishes. BMC Evolutionary Biology, 14, 1-9.
Mallet, J. (2001). Species, concepts of. Encyclopedia of biodiversity, 5, 427-440.
Mandeville, E. G., Hall Jr, R. O., & Buerkle, C. A. (2022). Ecological outcomes of hybridization vary extensively in Catostomus fishes. Evolution, 76(11), 2697-2711.
Ng, T. T., Sung, Y. Y., Danish-Daniel, M., Sorgeloos, P., de Peer, Y. V., Wong, L. L., & Tan, M. P. (2021). Genetic variation of domesticated discus (Symphysodon spp.). Aquaculture, Aquarium, Conservation & Legislation, 14(2), 832-840.
Schultz, R. J. (1969). Hybridization, unisexuality, and polyploidy in the teleost Poeciliopsis (Poeciliidae) and other vertebrates. The American Naturalist, 103(934), 605-619.
Santos da Silva, K., Glugoski, L., Vicari, M. R., de Souza, A. C. P., Noronha, R. C. R., Pieczarka, J. C., & Nagamachi, C. Y. (2022). Chromosomal Diversification in Ancistrus Species (Siluriformes: Loricariidae) Inferred From Repetitive Sequence Analysis. Frontiers in Genetics, 13, 838462.
Scribner, K. T., Page, K. S., & Bartron, M. L. (2000). Hybridization in freshwater fishes: a review of case studies and cytonuclear methods of biological inference. Reviews in Fish Biology and Fisheries, 10, 293-323.
Selz, O. M., & Seehausen, O. (2019). Interspecific hybridization can generate functional novelty in cichlid fish. Proceedings of the Royal Society B, 286(1913), 20191621.
Turner, B. J., Brett, B. L. H., & Miller, R. R. (1980). Interspecific hybridization and the evolutionary origin of a gynogenetic fish, Poecilia formosa. Evolution, 34(5), 917-922.
Quagio-Grassiotto, I., Baicere-Silva, C. M., de Oliveira Santana, J. C., & Mirande, J. M. (2020). Spermiogenesis and sperm ultrastructure as sources of phylogenetic characters. The example of characid fishes (Teleostei: Characiformes). Zoologischer Anzeiger, 289, 77-86.
When keeping an aquarium for the first time many are confronted with algaes, they cover the glass, plants, decor or even the water itself. Fishes that feed on algaes, known as algivores are often deployed here, sometimes mistakenly.
This I can only assume stems from the idea of a “clean up crew” and an aquarium ‘ecosystem’. The problem here is it is generalising algivores and misunderstanding this dietary niche in general because more then often we all keep algivores because they don’t fit the aesthetic we might not even know. Freshwater ecosystems are very complex and function cannot realistically be replicated in the aquarium.
Who are the algivores?
Algivores come from almost every branch of “fishes” from Cichlidae (Cichlids; Burress, 2016) to Siluriformes (catfishes). Even within these clades there is a wide amount of variation, in cichlids it’s quite obvious but in plecos, Loricariids there is a small number of carnivores and omnivores (Lujan et al., 2012). The actual mechanism of feeding varies a lot and this no doubt influences what algaes they can eat. Even within these groups there is a lot of variation in what algaes they will feed on (Delariva & Agostinho, 2001).
Both of these statements make sense when you buy algivores and they do not feed on some or all of the algaes that are causing an issue in the aquarium. Cyanobacteria makes the best example here, while many fishes do feed on it in the wild (Valencia & Zamudio; Baldo et al., 2019) it’s very evident they do not feed on the cyanobacteria that pests the aquarium, they are likely very different algaes. In many freshwater ecosystems there will be multiple species who feed on algaes and they could only co-exist if there was some partitioning in what algaes they feed on. Most of these fishes also feed on other microbes such as bacteria, protozoa etc. We even see divergent morphology likely based on what and the proportions of the different algaes and those other they feed on. This is where a common misconception comes, many will state that quite a lot of these fishes aren’t algivores because they aren’t ‘cleaning’ your aquarium.
So there is a lot of understanding the individual fishes to know what algaes they will eat and how much.
Another aspect here is the behaviour of algivores is often forgotten as they become more of a purpose then of a focus. Otocinclus, flying foxes (Epalzeorhynchos spp.) and Siamese algae eaters (Crossocheilus spp.) are shoaling and really do benefit from a minimum of 6 as shown here in the wild: https://www.inaturalist.org/taxa/98678-Crossocheilus-reticulatus/browse_photos. For Otocinclus they are shy when housed in small numbers, they are found in their hundreds in the wild. Epalzeorhynchos and Crossocheilus on the other hand in small numbers can become boisterous to each other and other fishes, there is no better example of this then E. bicolor. While for Otocinclus providing a group is rarely an issue for others it could be very limiting on aquarium size and particularly only to feed on one type of algae.
I can’t help but emphasize these fishes have their own requirements and they can be extremely specialized. Just because they feed on algae it does not mean they do not require a specialised environment based on their natural habitat. This is maybe why I see such a high mortality in certain species.
One thing never to forget is how long a fish might live and if it is only to solve an issue that might last a week or a few months you’ll have the fish years or even decades. Particularly catfishes, Loricariids/plecos, who are exceptionally long lived as often discussed in conversations:
Rehoming for some of these fishes can provide a particular challenge.
So what are the commonly recommended algivores:
Otocinclus sp.
Otocinclus spp.
Common name: Dwarf pleco, Oto
Locality: Widespread across South America (GBIF Backbone Taxonomy, 2023; Fricke et al., 2023)
Size: 16.5-43.8mm Standard Length (SL; Shaefer, 1997)
Comments: A small, shoaling (Axenrot & Kullander, 2003) genera found in clear, sandy waters with plenty of vegetation (Reis, 2004). This genus specialises in the finer algaes and other microbes growing on the variety of surfaces (Axenrot & Kullander, 2003). Otocinclus as a name has been used as a common name to refer to many other Hypoptopominae not all that stay that small, some such as Hypoptopoma incognitum at 9.4cm SL (Aquino & Schaefer, 2010). These other Hypoptopominae (The subfamily of Loricariidae that contains Otocinclus) are still just as social and some can be much more challenging to feed and sustain in captivity. I personally find particularly Rhinotocinclus and Nannoptopoma really suffer with the majority of ‘algae’ wafers where there isn’t a high amount of algae’s in the ingredient list. Otocinclus definitely do deal with the algae in an aquarium but not all such as black beard or cyanobacteria, after the algae is gone though they will need a more specialist algae based diet.
Common bristlenose, Ancistrus sp.
Ancistrus sp. ‘Common bristlenose’
Common name: BN, bristlenose pleco.
Locality: Unknown.
Size: 12-20cm SL, very variable.
Comments: This is a domestic species you’ll often see associated with Ancistrus cirrhosus or Ancistrus dolichopterus but it is related to neither of these species. As this species has been bred into many different variants from albino, super red, snow white to green dragon, there is additionally a lot of variation in size. It also makes any husbandry a lot more unpredictable as we neither know what the original species is nor can we really say how domestication has effected them. Unlike a few other Ancistrus this species is territorial and can take on any similarly shaped fishes if they enter their space, unlike many misconceptions this is regardless of sex. These do feed on algae but I can’t say they will deal with any on plants, nor black beard algae, cyanobacteria or most diatoms. Given how long these fishes can live and their size, certainly a consideration for any tank and they still have their own requirements.
Common name: Sharks, algae eaters and flying foxes.
Locality: East Asia.
Size: 12.46cm SL (Ciccotto et al., 2017) although individuals potentially grow up to 15cm SL in captivity.
Comments: As mentioned above generally social fishes who are boisterous with age in low numbers. They are brilliant in the right situation but temperatures definitely have to be considered for example the fishnet flying fox, Crossocheilus reticulatus who inhabits rapids and much cooler temperatures then generally expected. Certainly underrated fishes where they are almost never kept as the focus of an aquarium. Often noted to feed on black beard algaes but I’m not sure they are that rapid at it.
There are soo many fishes recommended and this changes with time such as the hillstream loaches, Gastromyzontidae who inhabit the rocky rapids of Asia but I might ask to look at these fishes in the wild and how specialised they are: https://uk.inaturalist.org/taxa/1032183-Gastromyzontidae/browse_photos
The actual problem, algaes
It is no doubt true that algaes can release toxins, these algaes have not been seen in the freshwater aquarium. Therefore, there is no real harm to algaes themselves excluding blocking filter inlets, outlets and sponges. More then anything algaes are a symptom of a variety of nutrients or conditions, some of them just might be an aquarium stabilising over the years.
Aquariums do have an ecosystem when it comes to microbes and with time the composition of these microbes will change. Aquariums don’t seem to really stabilise for years, obviously this likely wont have any scientific research behind it but if we look at natural ecosystems succession is a well known process. Succession is where the organisms change over time, while species diversity increases over time towards the end it then decreases. There is no same end goal to succession as it varies on so many factors and succession can be halted by certain species or environmental factors.
Of course the best method in the short term is likely really manually removing algae, this will likely effect this succession as removing the microbial populations that are competing with the algaes. Having worked in stores I use a variety of tools (ensure they are used for nothing else):
Scouring pad: Be careful on acrylic but this is great for most algaes and with a bit of hard work even diatoms.
Toothbrush: This is for the corners but can even work on decor. It can make a good attempt on blackbeard algae. Do not use too harshly on the corners as can damage and remove silicone.
Stanley blade: Definitely very sharp so be careful! Used wrong it can scratch glass and acrylic. Once you work out the right angle it’s great for removing any algaes such as diatoms and blackbeard on flat surfaces.
Filter Floss: Sometimes can be useful to clean large areas of soft algae, it can scratch the glass if catches sand granules but an easy thing to grab.
I personally do not recommend any of the magnetic algae cleaners due to the fact they tend to only remove the softest algaes and can easily catch sand, scratching the glass. T
Algaes themselves would deserve their own article but because of the polyphyletic (pick and mix) nature of the term between many very diverse groups of organisms, just because they are photosynthetic they aren’t simple.
I would treat algaes for mature aquariums particularly any sudden change in algaes present as biological indicators of nutrients, often ones we can’t or rarely test for.
The relationship between nutrients and algaes
Algal growth is inherently connected to nutrient composition. Unlike plants algaes can reproduce at a much more rapid rate taking advantage of any nutrients, the amount of algaes is usually connected to higher nitrate (Taziki et al., 2015) and phosphate levels (Fried et al., 2003). This makes sense as while a lot of rivers contain algaes which can contribute to the majority of the trophic interactions from photosynthesis, naturally rivers and lakes are oligotrophic (Lewis et al., 2001). Some of this nutrients we can’t help like nitrates out of the tap but when simply water changes which will benefit the health of the fish, what is the harm of that 30-60 minutes a week? Surely even a hamster, snake etc. takes more time. In another article I will probably discuss how to deal with when the source water is causing issues other then my article on RO.
Some sources of nutrients are easily forgotten, from certain botanicals to certain substrates. If it is the substrate usually it’ll be there from the beginning but adding certain botanicals like palms it’ll appear later on.
Conclusion
Algaes themselves are harmless and I think at some point we need to see them for what they are, maybe more interesting indicators.
References:
Aquino, A. E., & Schaefer, S. A. (2010). Systematics of the genus Hypoptopoma Günther, 1868 (Siluriformes, Loricariidae). Bulletin of the American Museum of Natural History, 2010(336), 1-110.
Axenrot, T. E., & Kullander, S. O. (2003). Corydoras diphyes (Siluriformes: Callichthyidae) and Otocinclus mimulus (Siluriformes: Loricariidae), two new species of catfishes from Paraguay, a case of mimetic association. Ichthyological Exploration of Freshwaters, 14(3), 249-272.
Baldo, L., Riera, J. L., Salzburger, W., & Barluenga, M. (2019). Phylogeography and ecological niche shape the cichlid fish gut microbiota in Central American and African Lakes. Frontiers in microbiology, 10, 2372.
Burress, E. D. (2016). Ecological diversification associated with the pharyngeal jaw diversity of Neotropical cichlid fishes. Journal of Animal Ecology, 85(1), 302-313.
Ciccotto, P. J., Pfeiffer, J. M., & Page, L. M. (2017). Revision of the cyprinid genus Crossocheilus (Tribe Labeonini) with description of a new species. Copeia, 105(2), 269-292.
Delariva, R. L., & Agostinho, A. A. (2001). Relationship between morphology and diets of six neotropical loricariids. Journal of Fish Biology, 58(3), 832-847.
Fried, S., Mackie, B., & Nothwehr, E. (2003). Nitrate and phosphate levels positively affect the growth of algae species found in Perry Pond. Tillers, 4, 21-24.
Lewis Jr, W. M., Hamilton, S. K., Rodríguez, M. A., Saunders III, J. F., & Lasi, M. A. (2001). Foodweb analysis of the Orinoco floodplain based on production estimates and stable isotope data. Journal of the North American Benthological Society, 20(2), 241-254.
Lujan, N. K., Winemiller, K. O., & Armbruster, J. W. (2012). Trophic diversity in the evolution and community assembly of loricariid catfishes. BMC Evolutionary Biology, 12(1), 1-13.
Otocinclus Cope, 1871 in GBIF Secretariat. GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2023-10-24.
Reis, R. E. (2004). Otocinclus cocama, a new uniquely colored loricariid catfish from Peru (Teleostei: Siluriformes), with comments on the impact of taxonomic revisions to the discovery of new taxa. Neotropical Ichthyology, 2, 109-115.
Schaefer, S. A. (1997). The Neotropical cascudinhos: systematics and biogeography of the Otocinclus catfishes (Siluriformes: Loricariidae). Proceedings of the Academy of Natural Sciences of Philadelphia, 148, 1-120.
Taziki, M., Ahmadzadeh, H., Murry, M. A., & Lyon, S. R. (2015). Nitrate and nitrite removal from wastewater using algae. Current Biotechnology, 4(4), 426-440.
Valencia, C. R., & Zamudio, H. (2007). Dieta y reproducción de Lasiancistrus caucanus (Pisces: Loricariidae) en la cuenca del río La Vieja, Alto Cauca, Colombia. Revista del Museo Argentino de Ciencias Naturales nueva serie, 9(2), 95-101.
This is certainly an example of a problem with common names, X. nigri is actually more closely related to Mormyrids and as Osteoglossiformes are very closely related to arowana. While mormyrids are electrosensitive not all members of this group are, the clown knifefish Chitala spp. lacks this ability. The name knifefish is given to a few members of Osteoglossiformes but that is a story of convergent evolution of shared morphology for a solution to a common problem particularly with those electrosensitive species. They are not at all related to true knifefishes, Gymnotiformes which are exclusive to South America and are distantly placed in the tree of life on the same branch as the catfishes (Siluriformes) and tetra (Characiformes; Hughes et al., 2018; Fig 1).
Figure 1: Phylogeny of ray-finned fishes, Actinopterygii produced by Hughes et al. (2018)
These Asian and African species known as knifefishes are very different in care as a result from Gymnotiformes. Many Gymnotiformes with very few exceptions are challenging to feed due to specialist morphology (Evans et al., 2019) and/or grow to exceptional sizes. While this is entirely also the case for Mormyrids. Regarding size the majority of these knife shaped Osteoglossiformes it leaves one Xenomystus nigri.
Common name: African Knifefish, Brown knifefish, African Brown Knifefish.
Scientific name: Xenomystus nigri Günther, 1868.
Origin: Wide spread from West Africa to Ethiopian, type locality is the Niger river. (Golubtsov & Darkov et al., 2008; Günther, 1868).
Size: 15.24cm SL (Günther, 1868) but there is a bit of variability around that, measurement converted from inches.
But why are these the best knifefishes for most people?
Size as I have already stated, 15cm SL as an adult is not a bad maximum size and a lot better then the 50cm SL black ghost knifefish, Apteronotus albifrons or any much larger species commonly available. They are easy to identify with the only similar species being the bronze featherback, Notopterus notopterus but thankfully X. nigri lacks a dorsal fin. So not easily confused with larger species unlike Gymnotus spp. who all are very similar in appearance. Many knives, true and not are territorial and do not tolerate each other particularly well, X. nigri is social and a shoaling species who is just fascinating to watch interact with each other but do keep in groups of more then 3.
To emphasise more, what makes Xenomystus nigri better then any other knife is how easy they are to feed. I brought my first individual before I really saw them around with bags of live food, little did I realise just after introducing the fish it was feeding on dry food. Many true knifefish, Gymnotiformes are a nightmare to feed, often with extreme gape limitation meaning the smallest of foods for a reasonable sized fish and even then they can be fussy. Due to the nature of how electrosensitive fishes feed by locating prey using electromagnetism (Waddell & Caputi, 2020), they might not even notice any food that is not live.
Habitat
It seems although a reasonably easy to locate fish there is no specifics on the habitat of these fishes. I’ve kept a few and can definitely say they need a lot of decor and hiding places. This makes them great fishes to watch as they move between everything in the aquarium.
I would provide a mixture of wood, rocks, branches and just many different places for them to retreat to. They do prefer dimmer lighting or even better would be areas of brighter and darker lighting so they have choice.
Water parameters
Unfussy, I can’t say much more given how widespread they are but given largely from West Africa softer more acidic and low conductivity water might be more ideal. They certainly do not suffer in higher conductivity water. It’d also be wrong to be specific or entirely certain as it’s generalising entire countries and water ways.
Sociality
As said previously these are extremely social fishes and do need to be in groups, by watching them you can see how much they interact closely with each other. In very small numbers such as a pair they can cause a lot of harm to each other.
Regarding tankmates avoid anything that can easily fit in their reasonable large mouth so small tetra but otherwise they are not aggressive.
Feeding
There is no doubt that electosensitive fishes are carnivores, plants do not produce such signals they can pick up. Realistically we can understand what these fishes feed on based on the mouth size, these are likely invertivores which might be more insect larvae but probably a small amount of smaller fishes. It’s very difficult without seeing any research into the diets of these fishes.
In captivity they have no problems being fed on a dry diet. Unlike feeding even a large range of live and frozen foods it is difficult to know how much nutrition the fish is really getting.
References:
Bullock, T. H., & Northcutt, R. G. (1982). A new electroreceptive teleost: Xenomystus nigri (Osteoglossiformes: Notopteridae). Journal of comparative physiology, 148, 345-352.
Evans, K. M., Kim, L. Y., Schubert, B. A., & Albert, J. S. (2019). Ecomorphology of neotropical electric fishes: an integrative approach to testing the relationships between form, function, and trophic ecology. Integrative Organismal Biology, 1(1), obz015.
Golubtsov, A. S., & Darkov, A. A. (2008). A review of fish diversity in the main drainage systems of Ethiopia based on the data obtained by 2008. In Ecological and faunistic studies in Ethiopia, Proceedings of jubilee meeting “Joint Ethio-Russian Biological Expedition (Vol. 20, pp. 69-102). Moscow: KMK Scientific Press.
Günther, A. C. (1868). Catalogue of the Fishes in the British Museum: VII (Vol. 7). order of the Trustees.
Hughes, L. C., Ortí, G., Huang, Y., Sun, Y., Baldwin, C. C., Thompson, A. W., … & Shi, Q. (2018). Comprehensive phylogeny of ray-finned fishes (Actinopterygii) based on transcriptomic and genomic data. Proceedings of the National Academy of Sciences, 115(24), 6249-6254.
Waddell, J. C., & Caputi, A. A. (2020). Electrocommunication in pulse Gymnotiformes: the role of electric organ discharge (EOD) time course in species identification. Journal of Experimental Biology, 223(16), jeb226340.
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