Little to common knowledge is that fishes are measured in multiple different ways and using different land marks to measure the fish from. These landmarks standardise any measurements and are frequently used in scientific papers over weight. The measuring of fishes is known as morphometrics, “morpho” coming from morphology the study of body shape and “metrics” coming from measuring.
Aspects of these measurements can be formal although many do provide a use in describing species and the landmarks used can be specific to particular taxa, groups. These measurements and as they change with age or between species, genera and families can tell us how fishes shape changes to the environment or allometric influences.
There are a few particularly common morphometrics that are most important as a fishkeeper to know:
Total Length (TL): This is the measurement from the tip of the head to the tip of the tail/caudal fin. This is the most problematic as caudal fins are commonly damaged and the length can be exceptionally and misleadingly long in some species or individuals. For example Panaqolus albivermis grows to around 12cm excluding this caudal fin but including the caudal fin and the extensions could bring it up to 20cm. Most reliable websites do not use this measurement.
Fork Length (FL): Very infrequently used in the aquarium hobby, this measurement goes from the tip of the head to the dip between the two lobes of a forked caudal fin. Similar flaws to total length but not all fishes have forked tails.
Standard Length (SL): As the name suggests this is the most reliable and common measure. Standard Length measures from the tip of the head to the end of the caudal peduncle or more easily remembered as to the base of the caudal fin. This measurement totally excludes the caudal fin and any variations with it. As this is the most reliable measurement reliable websites such as Seriously Fish, Planet Catfish, Scotcat etc. all use it even if they might not state it.
Head Length (HL): Rarely mentioned but worth just including, this is the measurement from the tip of the head to the end of the nuchal plate in Loricariids but seems to be end of the gill oppercula in others.
As people might have worked out there is a problem with these three measurements, many people are simply not aware they exist and therefore basing stocking and fish judgements on an incorrect measurement of length. For some species this misunderstanding might not make much of a difference but for some it could mean the difference between a 30cm fish and a 50cm fish.
It is also good to note that the metric system is used within science as it is the standard system and while many people use inches there is a reasonable difference in size particularly if choosing smaller fishes between each inch.
So why are these measurements used?
Well scientific papers and particularly species descriptions need standard units of measure. As hobbyists for many fishes particularly those who aren’t common or have not often been kept in the hobby we only have those scientific papers to go by on how big the fish gets. Sometimes we don’t even know potentially how long but these scientific papers will generally list the sizes of all the fishes they have caught. Assumptions can be made but do we want assumptions or honesty?
Many websites likely copy the length measurements of the reliable websites and do not transfer over how the fish are measured and this likely causes a lot of confusion.
Other Morphometrics
Maybe not so useful to aquariums apart from understanding physiology is there are many other measurements of fishes between different land marks all over the fish. These can be useful to identify certain fishes such as Panaque armbrusteri has a shorter pectoral fin then Panaque nigrolineatus (Lujan et al., 2010).
These measurements are generally what is specific to a group of fishes for example for Loricariidae we follow Armbruster (2009) as shown below:
Armbruster (2009) description of Peckoltia sabaji displaying the standard morphometrics used in Loricariidae.
1-20 here shows simple standard length and is probably the easiest way to visualise it. These measurements can show how shape changes between different species and individuals, Panaque for example would have deeper measurements around the head whereas Loricariinae will generally be slimmer and narrower.
Measurements are particularly useful for standardising, meaning everyone knows exactly what each other is talking about. Rather then me saying 15cm and someone saying 5 inches and another person saying 20cm. Scientists had long thought out and solved this issue but do state what measurements you are using hence you’ll see me say SL.
References:
Armbruster, J. W. (2003). Peckoltia sabaji, a new species from the Guyana Shield (Siluriformes: Loricariidae). Zootaxa, 344(1), 1-12.
Lujan, N. K., Hidalgo, M., & Stewart, D. J. (2010). Revision of Panaque (Panaque), with descriptions of three new species from the Amazon Basin (Siluriformes, Loricariidae). Copeia, 2010(4), 676-704.
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.
You might have heard the statement before, a fishes stomach is only the size of their eye. As a statement it comes from so many sides of truths, half truths and misunderstanding of fish biology.
I would argue the controversial, the majority of fishes we feed too little.
Corydoras bethanae (CW006) and Stendker discus, Symphysodon sp. taken at Maidenhead Aquatics, Wilton near Salisbury.
Largely the reason we don’t overfeed is to avoid overwhelming an aquarium with additional nutrients in the form of uneaten fish food that will decay, the results of that decay are handled by the microbes within the filter. The problem is where there is too much nutrients for those microbes in the filter to handle exposing the fish to it. Ammonia would be the main type of nutrients I am referring to but as we are talking about decay there is a lot more to it. This is the truth, it’s also quite logical but it means when we think about feeding we also need to think in terms of the microbes in the filter.
The stomach of fishes is hugely diverse (Pirhonen et al., 2019; Gosch et al., 2009) and in some species e.g. goldfish, Carassius auratus it is debated on it’s presence but largely the literature leads to the lack of it (McVay & Kaan, 1940; Kodzahinchex et al., 2018). The stomach size can be heavily linked to diet and the ability to specialise (Gosch et al., 2009). In the argument for eye size being related to stomach size, goldfish must lack eyes and imagine the eyes on the gulper catfish, Asterophysus batrachus if this was the case.
How much and how frequently should you feed your fish?
This has to be very species not just that but will have seasonal and allometric variations. There is no hard answer or even a formula, it’s an educated guess that can be narrowed down.
Baryancistrus demantoides, L200 also known as the green phantom or high finned green phantom pleco.
There is a multitude of studies suggesting that more frequent feedings to a point increase the growth of fishes (Fava et al., 2022; Cadorin et al., 2022). Anyone who has seen the two citations will see that farmed for the food industry feature heavily here. While research will always be focused on the highest investor, there is research into ornamental fishes. It’ll also be important to understand frequency and amount are different things, that one day frequency of food might be larger then what you’d feed 5 times a day or less then that.
In a study focusing on angelfish, Pterophyllum scalare by Ribeiro et al. (2012) 15 individual fish per a day were either 30, 60 or 90 grams per a kilogram of body weight, growth plateaued at 60g but 30g can sustain a fish without growth. In the Siamese fighting fish, Betta splendens weight only increased up to three times a day while in the guppy, Poecilia reticulata increased over four times a day, neither mentioned any amounts of food (Norazmi-Lokman et al., 2020). For the Rift Valley cichlid, Melanochromis aureatus growth rate was highest fed twice a day (Karadal et al., 2018).
Of course growth though is only one measure but to go into many others would complicate things and make the article maybe too long. Growth rate is a good all round measure as it can easily indicate how one factor, in our case amount/frequency of feeding influences many factors. Growth is heavily reliant on so many things from temperature, to specifical nutritional values, stress etc. but it does have it’s flaws as a measure.
Zebra pike cichlid, Crenicichla zebrina and I assume thresher plecos, Aphanotorulus emarginatus at Pier Aquatics, Wigan.
So what could effect feeding frequency:
Age, younger fishes need to devote a lot more to that growth period as they mature.
Breeding, individuals who are rearing young or maturing eggs need to devote more energy into those aspects of reproduction.
Temperature, the higher the temperature the more energy will be used and produced. This is more about the fishes optimal temperatures and range of tolerance.
Nutrition, a diet with a lower nutritional value will need to be fed a lot more frequently to reach the vital amount of nutrition required by the fish.
There is a misconception that animals generally have one meal every so often, particularly with fishes. This logically cannot be true, take grazing fishes such as discus (Symphysodon spp.), most Loricariids or even many ‘herbivorous’/algivorous/detritivores Rift Valley cichlids who devote large amounts of their time to obtaining food in smaller but frequent volumes (Crampton, 2008; Lujan et al., 2012; Hata et al., 2014). This is just by the nature of feeding on periplankton, algaes or detritus they are almost feeding like cows or rabbits. Although there is aspects of the Liems paradox where certain fishes can generalise and obtain a lot more nutrition in one sitting as seen in two species of grazing Tanganyikan cichlids (Golcher-Benavides & Wagner, 2019). Liems paradox likely has it’s limits though and doesn’t always play well in captivity where food items even if can be eaten can cause nutritional imbalances or issues with health.
Even within carnivores feeding frequency in the wild is going to vary. You can only watch Gymnotiformes, knifefishes and Mormyrids to see as many are micropredators but often at a larger size how often they are feeding. It reminds me of owls who need multiple food items in a day or shrews. They are constantly searching for food.
Giraffe catfish, Auchenoglanis occidentalis among many other fished, close up silver dollars, Metynnis sp. at Bristol Aquarium, Bristol.
Feeding frequency does add in questions of nutrition, higher nutritional items might not be need to be fed as frequently but another aspect of that is the rate of digestion which will be a limiting factor. So even if feeding a higher nutrition item, if a fish has a very rapid processing time how much of it will be digested? This is only amplified by food items that contain ingredients that cannot be digested or easy to digest. Such as the difficulty extracting phosphorus and calcium from fish as an ingredient by non-piscivores (Žák et al., 2022).
I personally feel that feeding frequency is behind the stunting of so many fishes particularly Loricariids. And catfishes maybe have lost out the most because there is the idea that they need feeding maybe once or twice a week but Loricariids, these cows of South America really do particularly at night show constant grazing. There was research into this grazing behaviour in Ancistrus sp. and given how much area they can clear and their ecological influence (Power, 1984), they are not once in a day feeders. Someone will argue but artificial captive diets are higher in nutrition, Ancistrus feed largely on algaes and a wide diversity (Lujan et al., 2012) but there is research on a few other species but very few diets (only 2) contain a noticeable amount of algaes. In a study 2017 study by Vucko et al. even just one species of algae replaced the entire commercial feed which if the ingredient list used by most brands. Not just are we not feeding Loricariids enough, we aren’t often feeding them what would be more then enough. Now why is there a claim that these fishes have a slow growth rate in captivity. I would definitely say Royal plecos, gold nugget plecos etc. do not have a slow wild growth rate.
The other aspect of these small feeding amounts is only feeding enough as x fish can eat in x amount of time usually a few minutes. Just watching how some fishes feed proves this wrong. There are many fishes I have kept and worked with who might take hours to reach their food and this will definitely cause harm with. Many are nocturnal or just don’t compete with other fishes.
How to avoid overfeeding?
I’m not sure what to really call overfeeding as there is no overfeeding unless resulting in obesity of the fish. But as it is more about overloading the bacteria with more fish waste or decaying material then they can handle, any increases in feeding should be handle. And if nitrates are peaking then more frequent and/or larger water changes. Sudden changes in feeding is more where issues arise and where water changes aren’t keeping up with the amount of food. Another thing to consider is the amount of waste produced and if the mechanical filtration can keep up or siphoning. I have not though mentioned how different food items and ingredients can heavily influence the amount of waste a fish is eating due to how much might not be digested, another story for another day.
How often you feed and the amount depends on the fish and understanding it’s biology and ecology. So again research is more then key here.
References:
Cadorin, D. I., da Silva, M. F., Masagounder, K., & Fracalossi, D. M. (2022). Interaction of feeding frequency and feeding rate on growth, nutrient utilization, and plasma metabolites of juvenile genetically improved farmed Nile tilapia, Oreochromis niloticus. Journal of the World Aquaculture Society, 53(2), 500-515.
Crampton, W. G. (2008). Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae). Neotropical Ichthyology, 6, 599-612.
Fava, A. F., de Souza Bezerra, G., Neu, D. H., Bittencourt, F., Signor, A., Carvalho, K. V., … & Boscolo, W. R. (2022). Effects of Feeding Frequency for Nile Tilapia Fingerlings (Oreochromis niloticus). Aquaculture Nutrition, 2022.
Golcher-Benavides, J., & Wagner, C. E. (2019). Playing out Liem’s paradox: Opportunistic piscivory across Lake Tanganyikan cichlids. The American Naturalist, 194(2), 260-267.
Gosch, N. J., Pope, K. L., & Michaletz, P. H. (2009). Stomach capacities of six freshwater fishes. Journal of Freshwater Ecology, 24(4), 645-649.
Hata, H., Tanabe, A. S., Yamamoto, S., Toju, H., Kohda, M., & Hori, M. (2014). Diet disparity among sympatric herbivorous cichlids in the same ecomorphs in Lake Tanganyika: amplicon pyrosequences on algal farms and stomach contents. Bmc Biology, 12, 1-14.
Karadal, O., Güroy, D., & Türkmen, G. (2018). Effects of feed type and feeding frequency on growth performance, reproductive efficiency and skin coloration of auratus cichlids (Melanochromis auratus). Aquaculture Studies, 18(2), 135-144.
Kodzhahinchev, V., Biancolin, A., & Bucking, C. (2018). Quantification of Mg2+, Ca2+ and H+ transport by the gastrointestinal tract of the goldfish, Carassius auratus, using the Scanning Ion-selective Electrode Technique (SIET). Plos one, 13(12), e0207782.
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.
McVay, J. A., & Kaan, H. W. (1940). The digestive tract of Carassius auratus. The Biological Bulletin, 78(1), 53-67.
Norazmi-Lokman, N. H., Baderi, A. A., Zabidi, Z. M., & Diana, A. W. (2020). Effects of different feeding frequency on Siamese fighting fish (Betta splenden) and Guppy (Poecilia reticulata) Juveniles: Data on growth performance and survival rate. Data in brief, 32, 106046.
Pirhonen, J., Muuri, L., Kalliokoski, S. M., Puranen, M. M., & Marjomäki, T. J. (2019). Seasonal and ontogenetic variability in stomach size of Eurasian perch (Perca fluviatilis L.). Aquaculture International, 27, 1125-1135.
Power, M. E. (1984). Habitat quality and the distribution of algae-grazing catfish in a Panamanian stream. The Journal of Animal Ecology, 357-374.
Ribeiro, F. D. A. S., Vasquez, L. A., Fernandes, J. B. K., & Sakomura, N. K. (2012). Feeding level and frequency for freshwater angelfish. Revista Brasileira de Zootecnia, 41, 1550-1554.
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.
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.
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.
This statement and those disagreeing features constantly in aquarium groups, websites, videos or any format. It’s such a well known saying with truths and untruths. The truths maybe as are as harmful as the untruths. So can fish grow to the size of the aquarium?
Here we have to really discuss stunting, the process at which growth is stalled or slowed down to one or more organs, tissues or anatomical parts. Here we are looking for causes not caused by malnutrition as that will cause changes in growth of fishes.
It is important to emphasize that the causes of reduced growth are not so much the size of the aquarium but the water it holds so aquariums where water is constantly being refreshed at a level that doesn’t result in a build up of certain compounds are exempt.
There are almost too many studies looking at stocking density and the growth of fishes, definitely inferring that the higher the stocking of fishes where water is not replaced anymore then the lower densities, the lower the growth rate (Björnsson & Ólafsdóttir, 2006; Maucieri et al., 2019).
The causes of this reduced growth rate are diverse and no doubt species dependent. Water quality is no doubt a large contributing factor as with higher stocking the lower the water quality and the more maintenance is required. In Björnsson & Ólafsdóttir (2006) the conclusion was ammonia was the largest cause of that reduced growth rate. While in a 2022 study it was suggested that low oxygen, pH, high ammonia, nitrite and nitrates all contributed to decreasing growth rate in the nile tilapia, Oreochromis niloticus (Abd El-Hack et al., 2022). And nitrite and nitrates particularly were found to reduce growth rate in grass carp, Ctenopharyngodon Idella (Zhang et al., 2023)
Outside of the contributions of fish waste to growth rate is the interaction between different species, higher densities in general and the social interactions, aggression or even without that can decrease or decrease growth rate depending on the species (da Silva et al., 2021). Pheromones are frequently mentioned in the aquarium hobby although I cannot seem to find any scientific research into their influence on growth rate, so should we assume either way?
Blue turk Stendker Discus, Symphysodon sp. with cyanobacteria.
There is a lot more to this story though, while there is the argument fishes can be stunted in the hobby what are the effects? No doubt this is largely species specific and depends on the cause of the stunting as certain compounds such as ammonia, nitrites, nitrates and oxygen will have different physiological effects. Many people probably falsely report the organs keep growing but the body does not, I can’t see this being physiologically viable but individual organ enlargement does seem reasonably common.
While not entirely relevant I feel it is particularly interesting where predation and food limitation occurred results in stunting of the rest of the body while the head grows closer to a normal rate and shape (Chizinski et al., 2010). This is so similar to the eye size reported in discus that are stunted. A study with quite the number of variables where goldfish, Carassius auratus were kept in a pond with a limited space displayed abnormalities differing them from wild/feral individuals (Almeida et al., 2008).
So do we have a conclusion here? I’m not entirely sure. We know that growth is effected by what the size of an aquarium usually entails such as poor water quality and increased stocking but that is not quite the same as growing to the same size as the aquarium. What I did miss is the many studies into how water quality increases mortality and is that maybe a lot more important? So regardless if a fish is stunted but has a higher chance of death that should be the real focus of appropriate aquarium size.
References
Abd El-Hack, M. E., El-Saadony, M. T., Nader, M. M., Salem, H. M., El-Tahan, A. M., Soliman, S. M., & Khafaga, A. F. (2022). Effect of environmental factors on growth performance of Nile tilapia (Oreochromis niloticus). International Journal of Biometeorology, 66(11), 2183-2194.
Almeida, D., Almodóvar, A., Nicola, G. G., & Elvira, B. (2008). Fluctuating asymmetry, abnormalities and parasitism as indicators of environmental stress in cultured stocks of goldfish and carp. Aquaculture, 279(1-4), 120-125.
Björnsson, B., & Ólafsdóttir, S. R. (2006). Effects of water quality and stocking density on growth performance of juvenile cod (Gadus morhua L.). ICES Journal of Marine Science, 63(2), 326-334.
Chizinski, C. J., Pope, K. L., Wilde, G. R., & Strauss, R. E. (2010). Implications of stunting on morphology of freshwater fishes. Journal of Fish Biology, 76(3), 564-579.
Maucieri, C., Nicoletto, C., Zanin, G., Birolo, M., Trocino, A., Sambo, P., … & Xiccato, G. (2019). Effect of stocking density of fish on water quality and growth performance of European Carp and leafy vegetables in a low-tech aquaponic system. PloS one, 14(5), e0217561.
da Silva, M. C., Canário, A. V. M., Hubbard, P. C., & Gonçalves, D. M. F. (2021). Physiology, endocrinology and chemical communication in aggressive behaviour of fishes. Journal of Fish Biology, 98(5), 1217-1233.
Zhang, J. M., Fu, B., Li, Y. C., Sun, J. H., Xie, J., Wang, G. J., … & Yu, E. M. (2023). The effect of nitrite and nitrate treatment on growth performance, nutritional composition and flavor-associated metabolites of grass carp (Ctenopharyngodon idella). Aquaculture, 562, 738784.
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).
Over generations as humans have eaten softer and softer foods it has resulted in the recession of the lower jaw (von Cramon-Taubadel, 2011). This was a discovery that really shocked people but I’m not really here to talk to you about humans. We are here for the fishes and in fishkeeping we aren’t so interested in change over such long time periods. The question is here, how does the hardness of the food we feed effect our fishes?
There is no doubt that a lot of the commercial diets are particularly soft whether it be pellets, wafers or flakes, this is only increased as foods become saturated with water. The hardness of foods must also be taken in respective to the species of the fish. Mode of eating would likely hold an influence to the hardness of food particularly when it comes to species that eat snails, there is a difference between whether the fish is extracting snails or crushing them. The hardness of the food a species might experience in the wild would definitely depend on what it is feeding on not just as the diet but also the surfaces it might be extracting food from e.g. sponges or wood.
Similar to humans fishes do show change in their jaw shape and morphology when fed a softer diet. In black carp, Mylopharyngodon piceus developed reduced pharyngeal jaws and pharyngeal arches which are involved in breaking down of food (Hung et al., 2015). Pharyngeal jaws are found at the back of the mouth of many fishes as a secondary pair of jaws involved in breaking down food whereas oral jaws that are visible externally are generally involved in prey/food item capture. Pharyngeal jaws might have teeth on them aiding in the breaking down of food, these jaws can be as diverse in a fish group as oral jaws. M. piceus in the wild frequently consume reasonable amounts of snails and mussels, interestingly when they do not have anything in their stomach they contain a lot of parasites previously carried by snails (Poulton et al., 2019).
Other factors are important though, food item hardness doesn’t always mean it is more difficult to break apart, maybe they require a bit more force. It’s always one thing to create an amazing diet but more importantly is will the fish eat it? Food item hardness potentially does effect how much food is eaten but the difficulty in being able to break apart the food is correlated with intake (Aas et al., 2020), perhaps it’s because the fish spend more time breaking it down?
There are other physiological effects of food hardness and durability, as it is broken down more easily in the water this can effect how quickly the fishes stomach can empty and reducing feed intake, Aas et al. (2020) suggested that the harder food takes longer to pass through the gut. A rather concerning aspect of this is the accumulation of fats in the stomach of salmon resulting in osmoregulatory stress from those softer diets that take up more water (Baeverfjord et al., 2006).
Of course it is important to mention there is a lot more to this, some fishes feed on naturally softer diets like a lot of algaes. Pufferfishes have a beak that is constantly growing and requires hard food items to keep that beak from becoming overgrown. The issue with puffer fishes is providing that range of nutrition without having an insane amount of different frozen foods, dry and gel diets generally contain a lot more of that range of nutrition.
An important part of hard against soft diets is water stability as previously mentioned before, as expected gel diets have a very high water stability (Lal et al., 2023). While it does seem counterintuitive there are ways of increasing the hardness of gel diets whether it be including harder items that require more processing or for the case of some fishes the diet can be added to the inside of a snail shell, a crab etc. On solid food items like a crab you could even smear the gel over the food item.
I feel this article has deterred from the original topic and largely this is because as a topic there isn’t much research into it. It does make sense for morphology to change as captive diet changes as well. So maybe it is more of something to think about for the future.
References:
Aas, T. S., Sixten, H. J., Hillestad, M., Ytrestøyl, T., Sveier, H., & Åsgård, T. (2020). Feed intake, nutrient digestibility and nutrient retention in Atlantic salmon (Salmo salar L.) fed diets with different physical pellet quality. Journal of Fisheries, 8(2), 768-776.
Baeverfjord, G., Refstie, S., Krogedal, P., & Åsgård, T. (2006). Low feed pellet water stability and fluctuating water salinity cause separation and accumulation of dietary oil in the stomach of rainbow trout (Oncorhynchus mykiss). Aquaculture, 261(4), 1335-1345.
von Cramon-Taubadel, N. (2011). Global human mandibular variation reflects differences in agricultural and hunter-gatherer subsistence strategies. Proceedings of the National Academy of Sciences, 108(49), 19546-19551.
Hung, N. M., Ryan, T. M., Stauffer Jr, J. R., & Madsen, H. (2015). Does hardness of food affect the development of pharyngeal teeth of the black carp, Mylopharyngodon piceus (Pisces: Cyprinidae)?. Biological Control, 80, 156-159.
Lal, J., Biswas, P., Singh, S. K., Debbarma, R., Mehta, N. K., Deb, S., … & Patel, A. B. (2023). Moving towards Gel for Fish Feeding: Focus on Functional Properties and Its Acceptance. Gels, 9(4), 305.
Poulton, B. C., Kroboth, P. T., George, A. E., Chapman, D. C., Bailey, J., McMurray, S. E., & Faiman, J. S. (2019). First examination of diet items consumed by wild-caught black carp (Mylopharyngodon piceus) in the US. The American Midland Naturalist, 182(1), 89-108.
Samuelsen, T. A., Hillestad, M., Jacobsen, H. J., Hjertnes, T. J., & Sixten, H. J. (2021). Physical feed quality and starch content causes a biological response in Atlantic salmon (Salmo salar L). Aquaculture Reports, 21, 100791.
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.
The Scientific Fishkeeper 