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.
When people think of plecos they think of the term ‘suckermouth catfish’, yet these are the total exception with little to no ability to attach to any surface.
Here I am referring to those Loricariids who spend their time largely on the substrate often with their ornate mouths with many long and short barbels also known as cirri (Rojas-Molina et al., 2019). Unlike most other Loricariids, plecos these fishes are not crevice spawners and in some species the ornate cirri are used by the males to hold the eggs (Corvain & Fisch-Muller, 2007). There is one exception here, I tend to classify Isorineloricaria and Aphanotorulus (previously known as Squaliforma) and largely known as the Thresher plecos, these are in the subfamily Hypostominae where the majority of well known Loricariids, plecos place. While the majority of this category are in the subfamily Loricariinae often known as whiptail catfish.
So this is not so much a nutritional, dietary category as much as to where they feed and to me that makes a massive difference. Scientifically there isn’t the greatest understanding of this group either but hopefully with future advances in the coming years we can. So obviously I will have to edit this one day.
Many of these species forage and locate food by processing the substrate a bit like Panaque process wood in search of their food. Using their jaws they filter food objects from that substrate. All of these species really need a sandy substrate, not just because many need to hide in it but also the enrichment of naturally removing food from it.
There are both algivores/detritivores and carnivores in this category. Ofcourse I definitely recommend reading my article on algivores and detritivores but their mode of feeding limits a lot.
Hemiodontichthys acipenserinus: Maybe a carnivore?
Isorineloricaria: Likely generalist detritivore.
Loricaria
Planiloricaria cryptodon: Either carnivore or feeds on seeds.
Pseudohemiodon: Suggested to be periplakton and algaes but could also feed on seeds.
Reganella
Rineloricaria (To an extent): Not exactly purely the substrate but do interact a lot with it.
There isn’t that many and I think this niche in many habitats are often catered for by other groups of fishes.
Anything these fishes feed needs to sink but that’s usually a given for Loricariids and ideally not large food items. Some of these genera have few to any teeth and very small jaws so cannot break into large food items. I’m not even sure we entirely know the actual mode of feeding they use and for research they are not the cheapest to obtain. For Isorineloricaria and Aphanotorulus their jaws are large and strong so it doesn’t make the largest amount of difference.
There are multiple genera here with morphology/anatomy that is unexplained, split between granivores (Seeds) or potentially molluscivorous (Gastropods like snails and bivalves) we just don’t know. We do know from a previous article that hardness of food items can matter so I think either way providing both would be beneficial, seeds such as from non-citrus fruits or apples, such as blue berries. Pest snails, no harm in having them as suggested in my snail article they can be a benefit. These are great snails for such species as easy for them to break down with the pharyngeal jaws.
When it comes to carnivores their interaction with the substrate does hint to them feeding on those invertebrates such as annelids and insect larvae that spend a considerable amount of time there.
It’s so difficult as we are making a lot of assumptions as to what they are eating and here I will treat them as the same. There is likely a lot of overlap at least. So as per the previous article into algivores and detritivores I highly recommend a good basic diet to build off. This will provide the essential nutrition to work off.
Anyway suggested basis diets:
Repashy Soilent Green and Bottom scratcher: Large diversity of algaes and high amounts of these algaes in Soilent Green. Bottom Scratcher on the other hand is very high in invertebrate items. They are higher up the list of ingredients so make up a lot of these diets. Easy to access for the majority of the world with many distributors. A gel diet so can be mixed to different consistencies and cooked to a jerky. It sinks and is very easy to break apart even if large by many of these species. The issue is what to which species if their diet is unknown.
In The Bag, Tropical Fish UK, Pleco Pops! Algae Grazer or Crickie-Dough: Over 75% algaes which is a very high amount for the algae based diet. The Crickie-Dough is even better I’d argue then bottom scratcher as high in crustaceans which is what most of these fishes would eat in the wild. While Repashy Bottom scratcher does provide a mollusc it is not closely related to gastropods or bivalves. Also a gel diet, the gelling agent used is brilliant as holds for an extremely long time, over 24 hours which is longer then any other gel food or one you can make your own. Cocoa powder is one is the most interesting and brilliant ingredients!
New Life Spectrum, Algaemax: Not to be confused with others of the same name so check the ingredients. Does contain a lot of algal ingredients but I can’t comment further due to UK availability.
C.E Essentials, Naturekind: While aimed at discus, Symphysodon it does contain a lot more algaes then other diets.
Should you make your own? You can but and that is a big but narrowing down the gelling agent that can last a few hours. This is difficult and takes time. Making your own diet commands research into nutrition and I’m really just only a beginner I think in that. It’s a large initial financial input as the ingredients particularly algaes are not cheap. This might be the only solution for some people in many countries and it is a debate for me how to help there.
Now to additions or supplements:
Frozen foods: A diversity of them would be brilliant so they can really feed off the substrate. Avoiding mussels as high in thiaminase and deficient in thiamine.
Live foods: Avoid any that move around the water column but those that focus in the substrate would be brilliant and offer more natural enrichment particularly black worms and tubifex.
Nori: Once it’s no longer a sheet I’d be inclined to suggest this as it rests in the substrate eventually, maybe not the best.
Earthworms: For larger species these might be found at the reptile store under the name Dendrobaena but definitely not to be missed. Do not forget though as they can survive underwater for some time if left and forgotten.
This sounds like a very limited list but compared to traditional algivores and detritivores frozen foods alone offers a lot more!
References:
Covain, R., & Fisch-Muller, S. (2007). The genera of the Neotropical armored catfish subfamily Loricariinae (Siluriformes: Loricariidae): a practical key and synopsis. Zootaxa, 1462(1), 1-40.
Rojas-Molina, Y. A., Provenzano-Rizzi, F., & Ramírez-Gil, H. (2019). A new species of whiptail armored catfish, genus Pseudohemiodon (Siluriformes: Loricariidae) from the Orinoco River basin, Llanos region of Colombia and Venezuela. Neotropical Ichthyology, 17, e180160.
This is a seriously large topic with 1,050 species according to Catalog of Fishes, so it’s not a simple answer. The majority of Loricariids are algivores and detritivores (Lujan et al., 2012). Even within detritivory and algivory there is partitioning (Lujan et al., 2011), this does mean they will not be feeding on the same thing. There is little research if to whether their diet changes with age but it seems there might be slight changes, certainly not towards any omnivorous/carnivorous diet as adults still had algae within their gut (Nonogaki et al., 2007), there is although evidence for seasonal shifts in diet (Mazzoni et al., 2010).
Baryancistrus xanthellus (Gold Nugget Pleco)
Here as I cannot really discuss all species and we are still in early days of understanding Loricariid diets I will present different categories with diets and suggestions to further supplement their diet.
It’s almost impossible to separate algivores and detritivores when it comes to Loricariids as there is so much overlap between the two categories but of course there is partitioning. It’s just we can’t really entirely cater for that partitioning. A lot of what is contained within detritus is this matrix of bacteria, protozoa, algaes and other microbes. In addition there are species who will feed more on algaes and some certain algaes like cyanobacteria e.g. Lasiancistrus caucanus (potentially L. mayoloi; Valencia & Zamudio, 2007), while others who might focus more on bacteria or fungi. We really don’t entirely know how much subdivision there is beyond the fact it exists. This is maybe the most fascinating dietary category as few other groups of fishes can do it like Loricariids can.
Chaetostoma sp. from Pier Aquatics, Wigan.
So, this category fills up the majority of Loricariids (Lujan et al., 2012) yet is maybe the most misunderstood or catered for. Bacteria, protozoa and other microbes are not really available in any commercial diets or even as ingredients which is very limiting leaving just algaes. We do know algaes are great in nutrition given just one species of algae replaced the nutritional requirements of a commercial diet which contained fish meal, cereals but only very few algaes in small volumes (Vucko et al., 2017).
The common misconception is that algaes are low in protein, yet they can be very high (Chen et al., 2022). This misconception comes from their similarity to plants but only green algaes are closely related to plants, while the term algae includes many other groups e.g. spirulina which is a cyanobacteria. Plants used in fish feeds might even lack many essential amino acids or contain anti-nutritional factors (Trevi et al., 2023). Algaes aren’t just high in protein but also very high in vitamins, minerals and essential fatty acids, to top the list of why algaes are great is their benefits on fish pigmentation (Alagawany et al., 2021; Trevi et al., 2023; Chen et al., 2022). So certainly an ingredient that shouldn’t be forgotten.
As we are talking fishes that feed on algaes as a large amount of their wild diets I can’t see how these simple ingredients are not useful. There is the issue of palatability and I have largely noticed they might struggle to recognise food not growing on a surface so in a wafer or pellet as algaes hence some taxa like those which are carnivores seem to do better then the very strict algivores.
So all we have to go off is a very small set of algaes but what should you look for in a main staple diet?
A main diet is what I see as the foundations of any fish food, this will contain all the main nutrition, vitamins and minerals. I understand additionally that different foods are limited around the world and cost also varies which makes it incredibly difficult for this dietary group.
Parancistrus aurantiacus (Xanto pleco)
What brands can I recommend as this basis to the diet, the foundations?
Repashy Soilent Green and Repashy Super Green: Large diversity of algaes and high amounts of these algaes, I believe 80% in Super Green. They are higher up the list of ingredients so make up a lot of these diets. Easy to access for the majority of the world with many distributors. A gel diet so can be mixed to different consistencies and cooked to a jerky.
In The Bag, Tropical Fish UK, Pleco Pops: Over 75% algaes which is a very high amount. Also a gel diet, the gelling agent used is brilliant as holds for an extremely long time, over 24 hours which is longer then any other gel food or one you can make your own.
New Life Spectrum, Algaemax: Not to be confused with others of the same name so check the ingredients. Does contain a lot of algal ingredients but I can’t comment further due to UK availability.
C.E Essentials, Naturekind: While aimed at discus, Symphysodon it does contain a lot more algaes then other diets.
Should you make your own? You can but and that is a big but narrowing down the gelling agent that can last a few hours. This is difficult and takes time. Making your own diet commands research into nutrition and I’m really just only a beginner I think in that. It’s a large initial financial input as the ingredients particularly algaes are not cheap. This might be the only solution for some people in many countries and it is a debate for me how to help there.
What genera are included in this (off the top of my head)?
Acanthicus (maybe, the rest of that group isn’t)
Acestridium
Ancistrus
Aphanotorulus
Baryancistrus
Chaetostoma
Cordylancistrus
Guyanancistrus
Hemiancistrus
Hypancistrus
Hypoptopoma
Hypostomus
Isorineloricaria
Lasiancistrus
Nannoptopoma
Otocinclus
Panaqolus
Panaque – Largely specialist for extracting microbes and fungi from wood.
Parancistrus
Parotocinclus
Peckoltia
Pogonopoma
Pseudancistrus
Pseudorinelepis
Pterygoplichthys
Rhinotocinclus
Rinelepis
Spectracanthicus – maybe excluding S. murinus
Sturisoma
Sturisomatichthys
Obviously I might forget a few or they aren’t even seen in the trade. There is also a lot we haven’t found on these fishes diets yet. I also haven’t included some that I put other niches for other reasons e.g. the substrate dwellers. I also can’t use common names as I’d end up making a list of hundreds for every common name there is.
Panaque nigrolineatus (watermelon pleco, one of the many Royal plecos)
Quick comment on wood ‘eaters’
These fishes have been proven as the article linked here cites to not digest wood or use it for digestion. Instead these genera Panaque, Panaqolus, the Hypostomus cochliodon group and Lasiancistrus heteracanthicus digest the microbes within wood in the wild but are just finding it in a different place. They do though consume and digest fungi. If wood within the aquarium had this diversity of microbes it’d decay very rapidly in captivity and it clearly doesn’t given a bit of wood can last years or over a decade.
So lets discuss supplements and additions to further cater for these fishes diets.
Vegetables: The most well known and there are always long lists of what they can be fed. They should never replace the algaes as nutritionally do not even compare as even suggested in Trevi et al. (2023). There is always a use in having something when a fish is skinny or newly imported and just feeding, I particularly find sweet potato and courgette great there but it shouldn’t be relied on. For larger species additionally as just padding out their diet and adding to. Given these fishes are rarely if ever feeding on plants in the wild then there is a lot of nutrition that is not easily accessible from plants.
Mushrooms: Now I separate these as the only fungi available to use aquarists, for those wood ‘eaters’; Panaque, Panaqolus, Hypostomus cochliodon group and Lasiancistrus heteracanthicus they can be of massive use given they feed on fungi in the wild. Potentially other algivores/detritivores might additionally feed on these but it is difficult to identify for many scientists if they do. I definitely recommend removing before 12 hours as it smells strong after being in an aquarium.
Additional algaes: Algae powders can be brought and can be mixed in with diets like Repashy soilent green or super green to bulk them up. Just bare in mind they might expire quicker then the Repashy and the amount of gelling agent might not be sufficient for it to hold well with other ingredients. I wouldn’t recommend adding much and any dried seaweeds would need to be blended.
Nori: All I can say is great if they will eat it but I think how easily it breaks down in the water column. So for some genera like Pterygoplichthys who are reasonably fast to feed it might actually work.
Seeds: These feature reasonably in Hypancistrus diets but given monocots and dicots covers most plants it could mean a lot (Armbruster et al., 2007). I think there is no harm in trying seeds such as sunflower seeds but also small low acidic fruits such as blueberries or blackberries. It could be that these fishes are actually consuming fruits. I have seen multiple examples where Loricariids do feed on these small fruits not just Hypancistrus but Panaqolus seems keen on these food items. I’d definitely not look to citrus fruits, large amounts of fruit and apple seeds are best avoided.
Growing rocks in the sun for algae: This can really work and is great for Otocinclus, it’s just being able to do so and the surface growing enough.
Botanicals: These could provide benefits but in large amounts or certain types add a lot of complexity to an aquarium. I find additionally the biofilms botanicals produce actually vary in how they appeal to different fishes. They definitely wont sustain anything other then maybe a few of the smallest fish.
Nettles: Potentially a great resource that needs to be explored more. Definitely dry than blanch for a few minutes in hot water for a few minutes to remove the sting.
General fish foods: These typical diets might not always be bad if bulking out a diet particularly during periods where a fish needs more food.
Gut Biota, what and why?
This is an emerging science regarding to biology but has barely touched the ornamental fish industry beyond probiotics should they work. There is a lot to unpack and I think there is a benefit in having other fishes and their waste providing gut biota. These gut biota might have been lost during importing or a period of stress and poor diet. As much as gut biota might change with introduction after stressful periods diet does also influence this.
The common bristlenose, Ancistrus sp. male.
Wood
I generally in my day job look at Loricariid diets in the literature and other then the previously mentioned genera have never seen wood in the guts of other species. It is not needed and even those species who consume wood as a byproduct do not use it for digestion (Lujan et al., 2011) so is not needed in a diet. Even more so cellulose and lignin were proven not to be digested or used in digestion and these are added into many diets, so these are more wasted space and added waste to any fishes diet.
At the end of the day these are massively misunderstood fishes as is their diet. There are many more Loricariids to understand here such as the carnivores and substrate feeders.
References:
Alagawany, M., Taha, A. E., Noreldin, A., El-Tarabily, K. A., & Abd El-Hack, M. E. (2021). Nutritional applications of species of Spirulina and Chlorella in farmed fish: A review. Aquaculture, 542, 736841.
Armbruster, J.W., Lujan, N.K. and Taphorn, D.C., 2007. Four new Hypancistrus (Siluriformes: Loricariidae) from Amazonas, Venezuela. Copeia, 2007(1), pp.62-79
Chen, F., Qian, J., He, Y., Leng, Y., & Zhou, W. (2022). Could Chlorella pyrenoidosa be exploited as an alternative nutrition source in aquaculture feed? A study on the nutritional values and anti-nutritional factors. Frontiers in Nutrition, 9, 1069760.
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), 1-13.
Mazzoni, R., Rezende, C. F., & Manna, L. R. (2010). Feeding ecology of Hypostomus punctatus Valenciennes, 1840 (Osteichthyes, Loricariidae) in a costal stream from Southeast Brazil. Brazilian Journal of Biology, 70, 569-574.
Nonogaki, H., Nelson, J. A., & Patterson, W. P. (2007). Dietary histories of herbivorous loricariid catfishes: Evidence from δ 13 C values of otoliths. Environmental Biology of Fishes, 78, 13-21.
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.
Vucko, M. J., Cole, A. J., Moorhead, J. A., Pit, J., & de Nys, R. (2017). The freshwater macroalga Oedogonium intermedium can meet the nutritional requirements of the herbivorous fish Ancistrus cirrhosus. Algal research, 27, 21-31.
Trevi, S., Uren Webster, T., Consuegra, S., & Garcia de Leaniz, C. (2023). Benefits of the microalgae Spirulina and Schizochytrium in fish nutrition: a meta-analysis. Scientific Reports, 13(1), 2208.
As inspired by a recent article in Practical Fishkeeping I feel I should again discuss a term used in fishkeeping too frequently yet lacks a true definition.
Sunshine/goldie pleco, Scobinancistrus aueatus and flagtailed characins, Semaprochilodus sp.
What is the community aquarium? The majority of fishkeepers would answer simply something along the lines of easy, peaceful fishes that can be kept together. This outlook is entirely flawed as stocking is more of a pick and mix with a lot of rules or educated judgements. No fish is entirely all the time peaceful. Take the simple and popular guppy, Poecilia reticulata can be nippy in the wrong context and males can hound females (Darden & Watts, 2012; Magurran & Seghers) or other fishes as they only have one thing on their mind, for slower feeding fish they are more then easily outcompeted by the swarm. So it is very context dependent. Take the neon tetra, Paracheirodon innesi as another alternative, for many fishes these like many other small tetra are easily predated on by other fishes.
Ease of care is very difficult to quantify or even evaluate, many of us have had particular species we for some reason have an issue keeping. For those maybe like myself who have specialised the jump between two species which might provide a challenge for a similar reason seems like nothing. I would argue research makes the difference, experience only goes so far because if you can’t research the fish any challenges will be unexpected or not responded to.
As a scientist the word community is very different and yet scientists have debated the definition of this name (Stroud et al., 2015). To those outside of the academic world they might not be familiar with how much science is argued and debated, that’s what makes it great as it is one big discussion to answer the biggest questions, there is still a level of right and wrong though before anyone questions the shape of the Earth. All of these definitions seem to largely work on an idea of a group of organisms living together at the same time and therefore likely interacting together. There is a functional effect to ecosystems and this is very different from aquariums due to the diversity of biotic and abiotic interactions in the wild.
So what is a community in the aquarium? I feel it saves a lot of hassle to be very broad as even just asking about community fishes is vague enough.
A community aquarium is a group of fishes that can be housed together. This is the more traditional definition hence you might see references to a predator community in the past. This definition separates it from species only, those fishes that can’t be housed with others for a variety of reasons. I would easily place freshwater and brackish pufferfishes under this category along with many predatory fishes who either are not gape limited e.g. Cetopsidae or do not house well with larger fishes they cannot eat. Then there is fishes like many Gymnotiformes or pipefishes that are soo slow to feed and need a lot of very small food items they might as well be species only unless for certain situations.
Only by understanding there is no community would we solve many of the issues with stocking choices and encourage research of every species added to the aquarium.
At the end of the day as I always say stocking is an art with a lot of judgement and educated guesses, research is important here. There is no stocking rules.
References
Darden, S. K., & Watts, L. (2012). Male sexual harassment alters female social behaviour towards other females. Biology letters, 8(2), 186-188.
Magurran, A. E., & Seghers, B. H. (1991). Variation in schooling and aggression amongst guppy (Poecilia reticulata) populations in Trinidad. Behaviour, 214-234.
Stroud, J. T., Bush, M. R., Ladd, M. C., Nowicki, R. J., Shantz, A. A., & Sweatman, J. (2015). Is a community still a community? Reviewing definitions of key terms in community ecology. Ecology and evolution, 5(21), 4757-4765.
The gold nugget, Baryancistrus xanthellus one of the most well known and popular Loricariids, plecos within the aquarium trade and maybe one of the most misunderstood. They are often challenging to keep and are rarely grown to maturity and even less frequently bred.
Baryancistrus xanthellus is a member of the genus Baryancistrus with a the type species being Baryancistrus niveatus, a species we do not see in the aquarium trade frequently. A type species is basically the species that defines the genus, in a way. There are 12 described species within this genus although phylogenetically/evolutionarly two of these do not belong in this genus, Baryancistrus demantoides and Baryancistrus beginni of which both are more closely related to the ‘Hemiancistrus’ clade (Lujan et al., 2015; Fig 1).
Figure 1: Phylogeny of Hypostominae featured in Lujan et al., (2015).
Because of this I wont be discussing either of those two species who are morphologically very different and their care is additionally different.
Additional to these described species are several undescribed species within the L number system, as many do not reach the aquarium trade the only undescribed species I’ll discuss here is Baryancistrus sp. ‘L142’
Like all Loricariids, Baryancistrus is exclusive to South America, the majority of this genus particularly is located in Brazil. They are a large bulky fish with a deeper head, not so much a defining feature because it is not present in all species and found also outside of the genus is a membrane between the dorsal and adipose fin. Their heads are not particularly wide but they are a strong appearing fishes. All species have spots to one degree or another, in Baryancistrus chrysolomus, the mango/magnum pleco these are rarely visible.
Like the undescribed species only two of the described species tend to occur in the aquarium trade so it would not be worth discussing the others.
So what are the three species:
Scientific name: Baryancistrus chrysolomus
Common names: Mango pleco, magnum pleco, L047
Adult size: 22cm SL (Py-Daniel et al., 2011), likely larger.
Origin: Rio Xingu
Temperature: 28c or higher (Rofrigues-Filho et al., 2015).
Water type: Clear water.
Habitat: Largely rocky with a strong current. Plenty of periplankton and sponges.
Adult size: 21.5cm SL but reports of individuals over 30cm SL (Py-Daniel et al., 2011).
Origin: Rio Xingu
Temperature: 28c or higher (Rofrigues-Filho et al., 2015).
Water type: Clear water.
Habitat: Largely rocky with a strong current. Plenty of periplankton and sponges.
Temperature
I can’t emphasise enough the importance of the higher temperatures with these species, particularly the two found in the Rio Xingu are not frequently exposed below 28c. More then often the water seems to be above 30c although oxygen saturation does decrease as the temperature increases so this needs to be thought of.
In my experience these fishes just don’t thrive lower. Temperature is known to be important in many biological processes not just gut biota function best at an optimum temperature but enzymes within the gut do too.
Water current
The habitat of these fishes has strong currents while rocks might act as refuge (Py-Daniel et al., 2011). The importance of a strong flow of water around the aquarium isn’t just for replicating their natural environment but also to maintain a higher oxygen saturation within the water as possible. The flow provides surface movement increasing gaseous exchange and circulates that oxygen around the aquarium.
Rocks or wood I don’t think it makes the difference, the main thing is about these fishes is plenty of caves and crevices. They really benefit from their own territory and spaces to hide. I always have plenty of caves for them as well but I recognise these are not available everywhere. For caves to try then Nature2Aqua has a brilliant range of caves and tunnels in a range of shapes and sizes and PlecoCeramics has some really nice designs.
There is no harm though in PVC caves as it’s about breaking up their enclosure and having ceramic caves is not important.
As you could maybe see of their habitat it does lack many plants with the exception of Podostemaceae, it’s a particularly challenging habitat for them. I would argue there is no harm in adding plants as long as the fishes needs are met. But these fishes will dig up any plants in the substrate and much of the fishes requirements conflict with that of plants.
Diet
This is the most interesting aspect of Baryancistrus. For some reason people see a colourful pleco/Loricariid and assume carnivore or omnivore. In no mean is Baryancistrus an omnivore. These fishes are quite strict algivores feeding almost entirely on algaes with the occasional invertebrate particularly bryozoans (Py-Daniel et al., 2011). Bryozoans are strange animals, like sponges they are filter feeding clonal organisms. It is additionally likely they are feeding on a wide range of other microbes. This is reflected in their jaw morphology, long with many numerous teeth is particularly noted in algivorous species (Lujan et al., 2012), one of the most extreme examples might be the hillstream Chaetostoma and Ancistrus. I can’t yet comment on their pharyngeal jaws, yes Loricariids have two sets of jaws.
This doesn’t sound like a specialist diet but it is, the algaes that grow in the aquarium do not grow enough and are more then often the wrong species. If aquarium algaes were enough then we wouldn’t see the failure rate we do. The other aspect is the amount of algaes in traditional captive diets, or just the majority is so very low usually being higher in cereals and fish/krill meal. I do recommend reading the ingredients of any fish food first!
So what should you feed them? This is a difficult question to answer and it is partially why I do not recommend this species. So what brands to consider:
Repashy: Great range of ingredients and wide range of algaes so a wider diversity of nutrition. For this species soilent or super green would be required. I have used this diet frequently to acclimatise fishes from the wild with great success. A gel diet but replicates their natural mode of feeding.
In the Bag, Tropical Fish UK Pleco Pops: Really high amount of algal ingredients and designed with Loricariids in mind. Again another gel diet.
Naturekind: While not designed for Loricariids it does provide a larger amount of algaes and is much more herbivorous then commercial brands.
Make your own: The one I least recommend, buying all the algaes is difficult and can get expensive. Gelling agents might not hold long enough and it is luck of the draw if the fishes even eat it. The biggest risk is getting that range of nutrition for the fishes.
It is really difficult in some countries and there becomes a kind of balance in regards to feeding for this genus and even most Loricariids.
Frequency of feeding Loricariids is almost always understated. These fishes are almost like underwater cows constantly grazing or eating with long digestive tracts. The algivores particularly this is no doubt the case. So for juveniles once a day would not be harmful but as the fish gets older more frequent feeding events would be beneficial. I would definitely leave courgette or mushrooms in between main feeding times but certainly not as a main diet.
Feeding at night is very important as it limits other fishes outcompeting for the food and these fishes are less likely to come out and feed with lights on.
These fishes are seriously slow feeders and will not compete with anything even slightly fast to feed. I have seen many issues when they are kept with fishes such as Geophagus, barbs or large Poecilidae (livebearer) groups. Definitely for many reasons why they should not be housed with very boisterous cichlids such as many of the popular Rift Valley cichlids.
Behaviour
Baryancistrus are very territorial, I have two/three adults and even before maturity disputes were not a rare occurrence. They are large and bulky and will through their weight around and for this reason large size disparities between individuals could result in issues. Plenty of caves and cover really does help here to break up the outline and prevent them frequently meeting each other but with time they will develop their own spaces they will keep to.
The aggression like other Loricariids is not just exclusive to other Baryancistrus. Slow moving tankmates who can’t move out the way are best avoided. But equally as much nothing very fast moving that can outcompete them for food.
Maintenance
I can definitely recommend a minimum of weekly water changes, these fishes want next to no nitrates or as little as possible, the same for any Loricariid.. They do seem to really thrive and survive on good water quality, not to say this shouldn’t be provided for any fish. I just feel it needs saying because of the popularity of certain aquarium methods.
Colouration
No doubt Baryancistrus are only popular for their striking and contrasting colouration. The seams found in two of them are half of that popularity and of all the colouration the seams will fade with age particularly the Baryancistrus xanthellus. Any spotting will reduce in size and these fishes tend to become a lot duller with age. But Baryancistrus xanthellus it is most obvious where the three L numbers people buy them for look the same as adults with minimal pin prick spots and little to no seams.
I have not described the different L numbers of Baryancistrus xanthellus and because of their adult colouration I don’t think it should matter. I also feel the L numbers are not reflective of the wild diversity nor of localities.
You might have noticed I have not mentioned sexing, that is a discussion for another article into sexing Loricariids. These members of the Hemiancistrus clade are a challenge and so few have mature enough fishes.
Baryancistrus are beautiful fishes but take considerable thought into their care with their adult size. They are not forgiving fishes and there are many smaller or easier to keep alternatives who also hold their colouration.
Lujan, N. K., Armbruster, J. W., Lovejoy, N. R., & López-Fernández, H. (2015). Multilocus molecular phylogeny of the suckermouth armored catfishes (Siluriformes: Loricariidae) with a focus on subfamily Hypostominae. Molecular phylogenetics and evolution, 82, 269-288.
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.
Magalhães, K. X., da Silva, R. D. F., Sawakuchi, A. O., Gonçalves, A. P., Gomes, G. F. E., Muriel-Cunha, J., … & de Sousa, L. M. (2021). Phylogeography of Baryancistrus xanthellus (Siluriformes: Loricariidae), a rheophilic catfish endemic to the Xingu River basin in eastern Amazonia. Plos one, 16(8), e0256677.
Py-Daniel, L. R., Zuanon, J., & Oliveira, R. R. D. (2011). Two new ornamental loricariid catfishes of Baryancistrus from rio Xingu drainage (Siluriformes: Hypostominae). Neotropical Ichthyology, 9, 241-252.
Rios-Villamizar, E. A., Piedade, M. T. F., Da Costa, J. G., Adeney, J. M. and Junk, W. J. (2013). Chemistry of different Amazonian water types for river classification: A preliminary review. Water and Society 2013, 178.
Rodrigues-Filho, J. L., Abe, D. S., Gatti-Junior, P., Medeiros, G. R., Degani, R. M., Blanco, F. P., Faria, C. R. L., Campanelli, L., Soares, F. S., Sidagis-Galli, C. V., Teixeira-Silva, V., Tundisi, J. E. M., Matsmura-Tundisi, T. and Tundisi, J. G. (2015). Spatial patterns of water quality in Xingu River Basin (Amazonia) prior to the Belo Monte dam impoundment. Brazilian Journal of Biology, 75(3).
This touches on a very controversial topic, what should you feed your discus fish? Strangely this fish has been described as a carnivore, an invertivore or an insectivore sometimes these myths are impossible to track down the origins. As a result traditionally for many years the answer has been beefheart, there is a lot to unpack about beefheart but equally as much about dry diets. No doubt that beefheart does result in weight gain (Reis et al., 2022; Wen et al., 2018) but it would not be fair entirely to compare it to dry diets given the diversity of dry diets out there. But this is half the story, these fishes are not carnivores in the wild.
Interestingly wild fish show a higher muscle protein content and crude fat was lower then domestic fishes (Wang et al., 2016) although I cannot identify the diet of those domestic fishes. So there is definitely a difference between these fishes, it could also be due to activity levels between the wild and domestic fishes.
There is only one paper specifically covering what these fishes eat in the wild, Crampton (2008). In this study the diet of Symphysodon “haraldi” was identified using gut analysis, as this species name is no longer valid (Amado et al., 2011) and the locality of these fishes being from the Rio Tefe these are probably Symphysodon tarzoo, the green discus identified by spots on the anal fin. This matters because there are other species of discus, Symphysodon aequifasciatus (Blue discus) and S. discus (Heckels) along with one undescribed species known as the blue discus and the undescribed Rio Xingu discus (Amado et al., 2011). Domestics result from a hybridisation of a variety of these species.
Figure 1: The diet of Symphysodon tarzoo (haraldi) in Crampton, W. G. (2008). Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae). Neotropical Ichthyology, 6, 599-612. FOD: Fine Organic Detritus, COD: Course Organic detritus. Periplankton is referred to as algae.
One can clearly see the seasonal variation in diets with a slightly higher contribution from invertebrates but still minimal. What is most clear though is the amount of detritus and periplankton these fishes are feeding on (Fig 1).
It is not just scientific research that has reported this, Bleher’s (2009) article on discus care also suggests this diet of mostly detritus. Detritus is a difficult term as a lot of it cannot be identified without a microscope, usually it seems in many fishes any loose or soft detritus generally is a microbial matrix, from my observations of research into Loricariids.
If we look at discus we can really think more about their diet.
Figure 2: Symphysodon tarzoo from the Rio Nanay, Peru.
These fishes are not the best built for prey capture beyond body shape lets focus on the anatomy that is most important for feeding. The jaws, and I don’t just mean upper and lower jaws. First looking at the mouth, they have a small mouth that cannot extend far, this means they are extremely limited on the size of item they can eat, this is known as gape limitation as many fishes including discus cannot chew with the oral jaws. They have strong lips great at removing food items from surfaces much like many other fishes who have a similar niche (Cohen et al., 2023). These are all factors connected with that first set of jaws, the oral jaws that really have a limited ability to expand outwards.
There is a second set of jaws, the pharyngeal jaws which are not immediately obvious as at the back of the mouth. Unlike the oral jaws that are about prey/food capture these pharyngeal jaws are about food processing. In discus these are thinner and more elongate (Roberts-Hugghis et al., 2023), not great at processing particularly solid food like large amount of invertebrates, also lacking the stronger villiforme or molariform teeth. Very similar to other detritivores or fishes feeding largely on algaes and detritus (Burress et al., 2020).
So, not just from their gut analysis but their morphology, Symphysodon are best classified along the lines of algivores and detritivores. You could say omnivores but if the mere addition no matter how small of any animal to any species diet makes them an omnivore then all organisms are omnivores.
From knowing this how should we see what we are feeding our fishes? Should we look to the inclusion of more algaes? And what algaes? What is the current long term effects of captive diets on discus?
There are brands such as Nature Kind by CE Fish Essentials who have started to look at wild diets and the inclusion of replicating that into their captive diet. https://cefishessentials.com/product/naturekind-fish-food-100g/ is the link for anyone who is curious.
Beefheart shouldn’t be the scapegoat for captive diets. Most commercial feeds as well differ massively from wild fish diets and there is a lot of questions to be asked about their use. Beefheart has proven itself as an effective captive diet though and many fishes live full lives on it.
So the story here is, read both what the fish eat in the wild and the ingredients of the food you are feeding.
References:
Amado, M. V., Farias, I. P., & Hrbek, T. (2011). A molecular perspective on systematics, taxonomy and classification Amazonian discus fishes of the genus Symphysodon. International Journal of Evolutionary Biology, 2011.
Burress, E. D., Martinez, C. M., & Wainwright, P. C. (2020). Decoupled jaws promote trophic diversity in cichlid fishes. Evolution, 74(5), 950-961.
Cohen, K. E., Lucanus, O., Summers, A. P., & Kolmann, M. A. (2023). Lip service: Histological phenotypes correlate with diet and feeding ecology in herbivorous pacus. The Anatomical Record, 306(2), 326-342.
Crampton, W. G. (2008). Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae). Neotropical Ichthyology, 6, 599-612.
Reis, G. A., Siqueira, M. S., & Momo, H. (2022). Evaluation of commercial and experimental grower diets for use in intensive culture of Symphysodon aequifasciatus. Pan-American Journal of Aquatic Sciences, 17(3), 190-200.
Roberts-Hugghis, A. S., Burress, E. D., Lam, B., & Wainwright, P. C. (2023). The cichlid pharyngeal jaw novelty enhances evolutionary integration in the feeding apparatus. Evolution, qpad109.
Wang, L., Chen, Z., Leng, X., Gao, J., Sun, P., Qu, H., … & Song, X. (2016). Comparison of muscle composition of wild and cultured discus fishes Symphysodon spp. Journal of Shanghai Ocean University, 25(5), 719-725.
Wen, B., Chen, Z., Qu, H., & Gao, J. (2018). Growth and fatty acid composition of discus fish Symphysodon haraldi given varying feed ratios of beef heart, duck heart, and shrimp meat. Aquaculture and fisheries, 3(2), 84-89.
Aquarium snails are one of the most popular invertebrates people keep within the aquarium, there is quite the diversity of forms and colours. They are generally very low maintenance and are not costly in their upkeep.
Snails are a common name for members of the Gastropoda who lack a shell and are in the family Mollusca which includes Cephalopods (Squids, cuttlefish and octopus), Bivalvia (clams, oysters and mussels) and a few lesser known clades. There are around 4,000 species of freshwater Gastropods, this value would include slugs due to there being no taxonomic difference and water bodies such as Lake Tanganyika or the Congo are hot spots for their diversity (Strong et al., 2008). There is a wide amount of diversity of shell morphology highly influenced by the habitat of these snails (Whelan, 2021).
Around 59 species of Gastropods are available within the aquarium trade, with 64% originating from Asia (Ng et al., 2016).
Ng et al. (2016) actually produced this amazing figure describing most if all of the Gastropods available within the aquarium trade although does seem to have some exceptions e.g. Asolene spixi.
All the aquarium Gastropods available in the aquarium trade as suggested by Ng et al. (2016) as followed by the text below.
When discussing snails we can’t help but discuss the diversity of snails labelled as pests, but what is a pest but a pet in the wrong place? Realistically we need to change our mind as to how we see these snails.
This common name covers a whole family of snails found throughout the world, they additionally vary in size massively. These snails clearly have much more fleshy tentacles. Image obtained from INaturalist and copyrighted to Herman Berteler under the Creative Commons licence https://creativecommons.org/licenses/by-nc/4.0/.
Ramshorn Snails (Planorbidae)
These snails display a very distinctive shell shape opposed to other pest snails although this is an entire family and additionally represents many ornamental species. Image belongs to Анатолий Кузьмин and sourced from INaturalist.
Pest snails get a very bad reputation, they generally come in on plants but sometimes by other means. These little Gastropods are generally harmless, they do not feed on plants nor will they attach to live fishes. In fact, they are great for any aquarium as they naturally feed on periplankton and detritus so act as a great indicator for overfeeding while helping further process any extra waste.
So lets discuss some of those more ornamental snails.
Rabbit/Elephant Snails (Tylomelania spp.)
Tylomelania spp. are some of my favourite aquarium snails. They are active, rummaging around the substrate and have a lot of different diversity in colouration originating from Sulawesi (Glaubrecht & von Rintelen, 2009). Like other viviparous snails they are diecious (individuals are not hermaphrodites) and produce one offspring at a time. These are detritivores/periplanktivores and while do not seem to feed on plants in the aquarium some are noted to in the wild (Rintelen & Glaubrecht, 2003), this could be due to the difference in species used.
These snails generally seem to interact with a sandy substrate and in the wild are located on silty substrates or on rocks or wood (Von Rintelen et al., 2007). Temperatures in the water bodies of these snails aren’t well known but seem to be stable around the 28-31c, these snails seem to be most common at the banks of the lakes where temperatures are around 28-29c (Vuillemin et al., 2016). I have kept them and bred many Tylomelania in unheated aquariums with no issues in breeding so safe to say they are certainly adaptable. In Vuillemin et al. (2016) the parameters of one of Tylomelania’s water bodies is described as having a pH of 7.8 and a conductivity of 210 μS cm-1. This does mean the water is a much lower conductivity then what would normally be expected at that pH.
Assassin Snail (Anentome helena)
Image source: Aquariumbreeder.com
While a very ornately coloured species of snail, assassins are some of the most aggressive in the freshwater trade. They are often used to feed on pest snails and they are definitely very good at this task but they will additionally feed on any ornamental snails. If not feeding on snails Assassin snails are capable of feeding on waste, food etc. While they are diecious they can lay an incredible number of eggs so can soon become the pest they are usually brought to prevent.
The most impressive of the ramshorn snails available to use in the aquarium trade, reaching sizes of 60-60mm (Grantham et al., 1993).
Although there seems to be no information on the habitats of this species, previous research has suggested that Columbian Ramshorn snails do best around 25c (Aufderheide et al., 2006). The downfall as with many Ampullariidae such as Asolene spixi is their very diverse diet of not just a diversity of plants (Seaman & Porterfield, 1964) but it seems snail eggs too (Demian & Lutfy, 1965). These are definitely snails to eat your plants.
White Wizard Snail (Filopaludina martensi)
Image source: Aquarium Glaser GmbH
What can I say more about Viviparidae snails other then them being really charming inhabitants, I have discussed Tylomelania probably the easiest to keep so now one that requires more thought.
Filopaludina martensi are no doubt some of the most attractive snails in the aquarium hobby and realistically everything I say for Tylomelania regarding breeding stands true here. They will not overpopulate any aquarium with any speed and easy to rehome individuals should they do. Unlike Tylomelania who do not seem to display any sexually dimorphic features, F. martensi displays a modified tentacle in males and a larger shell size in females (Sawangproh et al., 2021).
They are a little bit more challenging as seem to require much more periplankton and detritus within the aquarium and are not keen to feed on any other foods provided. It seems in the literature they are suggested as filter feeders and this could explain why, although lacking citations or personal observations detritivore might be more accurate (Piyatiratitivorakul & Boonchamoi, 2008). By observation of this snails anatomy I would definitely say detritivore, it has no filter feeding apparatus maybe apart from the gills. It does seem very little is known about this snails ecology. Although one of the catch localities, Kwai Yai River (Sawangproh et al., 2021) for this snail records temperatures of 22-33c showing these snails are adaptable to a wide range of aquarium temperatures (Leelahakriengkrai & Peerapornpisal, 2011).
Obviously I cannot talk about all 59+ Gastropods within the aquarium trade and a lot of information will be species or taxa specific. So I will discuss some misconceptions.
The importance of calcium?
There is no doubt much like fish Gastropods utilise calcium to build their shells and for other physiological processes. Gastropods like fishes can uptake calcium from the water and also from their food but their ability to do so depends on the species. Snails have been split into two categories, those that require it in the water and those that can live in low calcium and utilise calcium from their food (Dalesman & Lukowiak, 2010). So you really need to look at individual species and considering the importance of calcium volumes within the water. The use of a calcium block, cuttlefish bone or any snail food wont replace what is required in the environment for those species. And for species that obtain calcium from their diet consider they are actually getting calcium in their diet.
Does diet matter?
I think this just has a simple answer, yes. Snails generally are amazing opportunists and many can eat a wide range of resources. Research your snail before you buy as there are some more challenging species as mentioned earlier. There are so many creative ways to feed aquarium Gastropods and this maybe needs it’s own article later on as you can easily get away without so much.
References
Aufderheide, J., Warbritton, R., Pounds, N., File‐Emperador, S., Staples, C., Caspers, N., & Forbes, V. (2006). Effects of husbandry parameters on the life‐history traits of the apple snail, Marisa cornuarietis: effects of temperature, photoperiod, and population density. Invertebrate Biology, 125(1), 9-20.
Dalesman, S., & Lukowiak, K. (2010). Effect of acute exposure to low environmental calcium on respiration and locomotion in Lymnaea stagnalis (L.). Journal of Experimental Biology, 213(9), 1471-1476.
Demian, E. S., & Lutfy, R. G. (1965). Predatory activity of Marisa cornuarietis against Biomphalaria alexandrina under laboratory conditions. Annals of Tropical Medicine & Parasitology, 59(3), 337-339.
Glaubrecht, M., & von Rintelen, T. (2009). The species flocks of lacustrine gastropods: Tylomelania on Sulawesi as models in speciation and adaptive radiation. In Patterns and Processes of Speciation in Ancient Lakes: Proceedings of the Fourth Symposium on Speciation in Ancient Lakes, Berlin, Germany, September 4–8, 2006 (pp. 181-199). Springer Netherlands.
Grantham, Ö. K., Moorhead, D. L., & Willig, M. R. (1993). Feeding preference of an aquatic gastropod, Marisa cornuarietis: effects of pre-exposure. Journal of the North American Benthological Society, 12(4), 431-437.
Leelahakriengkrai, P., & Peerapornpisal, Y. (2011). Water quality and trophic status in main rivers of Thailand. Chiang Mai Journal of Science, 38(2), 280-294.
Ng, T. H., Tan, S. K., Wong, W. H., Meier, R., Chan, S. Y., Tan, H. H., & Yeo, D. C. (2016). Molluscs for sale: assessment of freshwater gastropods and bivalves in the ornamental pet trade. PLoS One, 11(8), e0161130.
Piyatiratitivorakul, P., & Boonchamoi, P. (2008). Comparative toxicity of mercury and cadmium to the juvenile freshwater snail, Filopaludina martensi martensi. Sci Asia, 34, 367-370.
von Rintelen, T., Bouchet, P., & Glaubrecht, M. (2007). Ancient lakes as hotspots of diversity: a morphological review of an endemic species flock of Tylomelania (Gastropoda: Cerithioidea: Pachychilidae) in the Malili lake system on Sulawesi, Indonesia. Hydrobiologia, 592, 11-94.
Vuillemin, A., Friese, A., Alawi, M., Henny, C., Nomosatryo, S., Wagner, D., … & Kallmeyer, J. (2016). Geomicrobiological features of ferruginous sediments from Lake Towuti, Indonesia. Frontiers in Microbiology, 7, 1007.
Rintelen, T. V., & Glaubrecht, M. (2003). New discoveries in old lakes: three new species of Tylomelania Sarasin & Sarasin, 1897 (Gastropoda: Cerithioidea: Pachychilidae) from the Malili lake system on Sulawesi, Indonesia. Journal of Molluscan Studies, 69(1), 3-17.
Sawangproh, W., Phaenark, C., Chunchob, S., & Paejaroen, P. (2021). Sexual dimorphism and morphometric analysis of Filopaludina martensi martensi (Gastropoda: Viviparidae). Ruthenica, Russian Malacological Journal, 31(2).
Seaman, D. E., & Porterfield, W. A. (1964). Control of aquatic weeds by the snail Marisa cornuarietis. Weeds, 12(2), 87-92.
Strong, E. E., Gargominy, O., Ponder, W. F., & Bouchet, P. (2008). Global diversity of gastropods (Gastropoda; Mollusca) in freshwater. Freshwater animal diversity assessment, 149-166.
Whelan, N. V. (2021). Phenotypic plasticity and the endless forms of freshwater gastropod shells. Freshwater Mollusk Biology and Conservation, 24(2), 87-103.
Mother Earth has been a concept for a long time but the scientific concept of life being self regulating was largely coined by the late Dr. James Lovelock in a theory known as the Gaia Hypothesis. This hypothesis captured life’s nature to recover and the interconnected system between organisms. Although later combated or maybe better complicated by the Medea hypothesis theorised by Professor Peter Ward and the popular book, The Selfish Gene by Dr Richard Dawkins. These two theories encapsulate the complex nature of life itself and the many mass extinction events caused by species in that fight for life and reproduction.
Survival is argued as not altruistic regardless if competing with members of your own species or another. There is a constant battle not just between predator and prey but between competitors for resources such as space. This battle is not just found in the animal world though, plants fight for space and use a variety of mechanisms to do this.
But how does this effect us in the aquarium hobby? Just by the selfish nature of organisms we can’t look at each organism providing a role, that’s not how nature works and it ignores that species provide multiple interactions. Plants don’t just photosynthesise but they constantly respire and also utilise minerals within the water. These plants might then compete with each other and maybe a fish for a variety of these resources. To compete with plants many develop methods to block out light but in that competition for space other methods might be utilised, plants like many other organisms potentially utilise chemical warfare.
Within animals when people think about purposes particularly pests they might not just interact as ideally wanted, loaches that feed on snails might take smaller fishes.
In the aquarium I feel we have to balance this constant battle. Everything using oxygen, feeding on nutrients and space.
While I’ve provided no citations it’s more a food for thought short communication essay.
There is no doubt goldfish, Carassius auratus is one of the most adaptable fish species. While the parent species being either/or the Prussian carp, C. gibelio or the Crucian carp, C. carassius are proven without a doubt to adapt to a range of climates the goldfish on the other hand is treated as the sensitive child. Well, not all goldfish but this is very much a cherry picking of different varieties thrown into hardy or not.
First lets split the goldfish up:
Single tails
Common/hibuna: This is the typical goldfish with the short single caudal fin.
Comet: Displays a more elongate caudal fin that might be more ribbon shaped.
Shubunkin: This is a variety that is split into multiple different subvarieties depending on caudal fin type. The London shubunkin has a shorter caudal fin, the common body and tail shape. The Japanese shubunkin has that comet caudal fin shape. The Bristol shubunkin being unique with a large elongate but heart shaped caudal fin that holds it’s height and shape. The difference between the shubunkin and the first two is the calico patterning, black, red, orange and blue.
Tamasaba and sabao, shorter ryukin shaped goldfish with white and red patterning originally bred by Japanese koi breeders. The Tamasaba has the longer caudal fin.
Nymph, not so much a variety but a undesirable mutation of the double tailed varieties where a number of single tailed individuals are produced.
Double tailed, this is produced by a duplication event (Abe et al., 2014).
Wakin: Very similar to the common goldfish but with a double tail. Not to be confused with mutations in commons, comets and shubunkin resulting in a double tail, I have seen full to partial splits at least 3 times, the wakin seems to have more of an arch to the spine at the back.
Jikin: Similar to the wakin but deeper bodied, seems to lack that arching and with more of a flower shaped caudal fin. It is strictly red and white, ideally with 13 points of red but this is produced by certain methods.
Fantail: The most famous and varies on quality or how much it matches the standards. This variety by standard should be deeper bodied but has a short heart shaped caudal fin.
Oranda: There are multiple subvarieties from goosehead to lionhead oranda, this variety is a deep bodied fish with fatty growths covering the head or the top of the head. Caudal fin shape also varies depending on standard and variety from a straight long veiltail to a short heart shaped caudal fin.
Ryukin: An extreme deep bodied and described by the GSGB (Goldfish Society of the British Isles) as having a bulldog like appearance, it has a hump behind the head resulting in it’s unusual appearance. Despite the name it is not originally Japanese as having originated from China arriving via the Ryukyu Islands, quite a few varieties often thought of as Japanese have Chinese origins.
Lionhead: As of recent an uncommon variety, most sold under this name are in fact low quality oranda. It should have a large fatty head growth like the oranda but lack a dorsal fin and have a straighter back.
Ranchu: There are multiple varieties of this, the original Japanese ranchu is known as the top view ranchu, uncommon outside certain exporters. Like most true Japanese fish to be judged from above. Lacks a dorsal fin with a nice smooth arched back, short caudal fin and an attractive fatty head growth. Side view ranchu are common in the trade.
Tosakin: A rare variety in the UK, very similar to a fantail but has a long caudal fin that is spread out in a butterfly shape to be viewed from above. Reached close to extinction in Japan but is making a recovery.
Izumo nankin: A rare variety, similar to the ranchu in it’s deeper body but lacks any head growth. Red and white patterning in a desired pattern.
Veiltail: Uncommon outside the show scene, has a broad, lacking that forking long caudal fin otherwise similar to the fantail.
Moor: A telescope eyed variety, it generally in the UK has a veiltailed caudal fin to be standard and must have more triangular eyes.
Globe eye: Similar to the moor in being a telescope eye but the eyes are rounded, the tail can be short or long but generally rounded and forked. Demekins do somewhat fall under this but are almost like a cross between the ryukin and globe eye.
I didn’t list these varieties for no reason, body shape is extremely diverse between each and therefore the split only means a difference in whether there is two or one caudal fin. Fancy usually refers to any goldfish but the comet, shubunkin and common which if you get what I mean it really means very little as a term.
There is a long history of goldfish’s being kept and bred outside in not just Japan and China; but also Thailand, Java, the UK and the USA. It is not difficult to find this in societies alternatively in a greenhouse.
I myself have kept a variety of fancies outside year round but it requires serious thought.
What benefits could keeping goldfish outside have?
The major obvious one is colouration, natural lighting perhaps it’s the UVB really enhances black pigmentation (melanin) in goldfish or preventing any loss. Any green water encourages red colouration.
Potentially more natural food sources, many insects and invertebrates naturally become introduced to ponds.
Natural seasonal cycles like they would have experienced as a wild species, it gives them a period of rest. It is obvious how seasonal these fishes are in the fact they spawn with seasonal temperature ques.
The opportunity and ease of providing more space, ponds are generally cheaper then aquariums. This can allow for much more enrichment.
Considerations
Goldfish still need water changes and filtration in a pond regardless of plants or setup.
Only add fishes to ponds in the warmer months, May to September (based on UK temperatures), ideally 15-18c or above giving them plenty of time to adapt to temperature drops later on in the year and avoiding sudden frosts.
Over winter and when temperatures drop the fishes will have a reduced appetite and reduced metabolism so feeding is best reduced slowly to a stop in winter to prevent any rotting of uneaten food. When temperatures increase again the fish can be fed again. Water changes aren’t required when the fishes have such a drop of metabolism.
Goldfish are susceptible to predators so netting or grids above the pond is a must.
While goldfish are more then capable of going anaerobic during periods of cold extreme cold resulting in a deep and thick ice layer should be considered in countries where this occurs. This might mean any fishes being taken inside between September to May. Depth of pond is also important as the bottom will create a refuge for the fishes, shallow is much better for body shape but the temperature will drop much more rapidly.
Any fishes displaying swim bladder disorders should be removed and kept inside as the heat or cold can damage any floating fish.
In summer a good filter should create enough aeration and goldfish can gulp but an air pump or fountain would be important to maintain oxygen levels.
You can see it’s not so simple but it doesn’t mean it’s bad to keep them outside. The importance of natural cycles is potentially very understudied and underrated within the aquarium hobby. Potentially it could even lead to a longer lifespan and healthier fishes but we don’t really know?
Both goldfish considered fancy and not are both farmed in hotter climates then ours in the UK so there isn’t so much logic behind their perceived variance sensitivity excluding the limited gene pool of some.
References
Abe, G., Lee, S. H., Chang, M., Liu, S. C., Tsai, H. Y., & Ota, K. G. (2014). The origin of the bifurcated axial skeletal system in the twin-tail goldfish. Nature communications, 5(1), 3360.
Biological/Biochemical Oxygen Demand (BOD) is a topic we never discuss in the hobby, it refers to largely to the amount of oxygen that aerobic microorganisms use to remove or process waste (Brenniman, 1999) and are directly connected with oxygen saturation and nitrate concentration (Alam et al., 2020).
In a way the hobby talks so little about decomposition focusing on other aspects of nutrient cycling. For a fishkeeper that water changes, siphons and leaves little to no waste or items decaying in the aquarium it might not be of concern.
Botanicals and planted tanks are very popular as of recent with people reaching for some idea of nature they feel they have lost, natural or not. Both of these setups can allow for the trapping of waste where siphoning is not possible or limited. One solution is reduced stocking but definitely keeping fishes adapted for low oxygen saturations is a great solution such as airbreathers.
Decomposition of material such as decaying plants or botanicals involve bacteria, protozoa and other microorganism’s. It’s not just these as an introduction of nutrients but also anything that can be used as a nutrient source for bacteria, I find particularly sugars and carbohydrates. We can split them between aerobic (With oxygen) and anaerobic (without oxygen), anaerobic is another topic here but it does involve the production of other compounds. Just because there is a thick layer of substrate it doesn’t mean it is anaerobic particularly with the presence of plant roots that encourage oxygenation. We also don’t know the rate of either and this will depend on a variety of factors.
These microorganisms are more then capable of competing with fishes for oxygen and the rate will depend on multiple conditions (Nolan, 1996; El-Moghazy & El-Morsy, 2017). Microorganisms can proliferate much faster then fishes so can quickly adapt and increase to those higher nutrient levels.
The issue is that we can barely measure BOD but we can measure oxygen saturation. This means it is difficult to experiment the BOD within any aquarium so we do have to make assumptions.
Most of these are purely assumptions and ideas based on previous knowledge as it’s not so much a topic that the literature will look into. It’s also something fishkeepers certainly need to be thinking about or considering particularly for heavily stocked tanks or fishes who uptake a lot of oxygen.
Temperature, oxygen saturation and decomposition rate
It is a well known effect that as temperature increases oxygen saturation in turn decreases although when thinking about decomposition this increases as microbial decomposers can proliferate at a much faster rate and consume their resources further. This could result in further BOD when there are already low levels (El-Moghazy & El-Morsy, 2017).
Generally it’s better safe then sorry so removing detritus that has built up in the tank and within the filter. Decomposers are probably only providing a benefit maybe for plants but for fishes in many aspects discussed previously they are not of benefit. Any botanicals or high nutrient imputs should be added gradually over time so not to unload a lot of nutrients into the aquarium or when decaying again as much nutrients for these microbes and reducing oxygen saturation.
While we don’t have values and honestly, there is no way of doing that as every aquarium is difficult it’s difficult to predict.
References
Alam, M. S., Han, B., Gregg, A., & Pichtel, J. (2020). Nitrate and biochemical oxygen demand change in a typical Midwest stream in the past two decades. H2Open Journal, 3(1), 519-537.
Brenniman, G. R. (1999). Biochemical oxygen demand. Environmental Geology. Encyclopedia of Earth Science. Springer, Dordrecht. https://doi. org/10.1007/1-4020-4494-1_34.
El-Moghazy, M. M., & El-Morsy, A. M. (2017). Effect of water aquaria changes on growth performance of Nile tilapia Oreochromis niloticus and the relationship between bacterial load and biological oxygen demand. International Journal of Fisheries and Aquatic Studies, 5(3), 341-349.
Nolan, C. (1996). Ventilation rates for carassius auratus during changes in dissolved oxygen.
The Scientific Fishkeeper 