Bloodworm has been a food that has been discouraged against for around 10 or more years. There has never been any doubt that many fishes feed on Chironomatid larvae in the wild (Delariva & Agostinho, 2001; Valtierra-Vega & Schmitter-Soto, 2000), even discus feed on them (Crampton, 2008). Chironomatid larvae being the more scientific name for bloodworm. You might have even seen these larvae in your pond, buckets or similar.
Bloodworms as featured in: Paice, R. (2016). Assessment of mosquito larvicide impacts on aquatic invertebrates in the Vasse-Wonnerup Wetland System.
So why are bloodworms so feared?
I don’t think there is a true origin to this, it is still one of the most common live and frozen foods used, it’s cheap and easy to find. Maybe there are still some aspects of when tubifex was feared due to sewage contamination.
Bloodworm being the larvae of an insect does have a casing, known as an exoskeleton formed of chitin. This can be difficult to digest and for some fishes impossible, although many species are possibly sold as bloodworm it’s likely there is some diversity. There are reports of constipation and similar caused by bloodworm, although bloating is tricky and can have many causes from bacterial infections to a food item not being processed.
Bloodworm is not the entire diet of any fishes I’ve researched and when fed as an entire diet it results in liver enlargement and and poorer body condition (Žák et al., 2022), these results are similar to Hao et al. (2021) where removing to a formulated diet increases general health of the fish.
I chose this topic to find reasons that I am wrong, that bloodworm is much better then I thought it was. It doesn’t seem bad for fattening up fishes but does seem to come with a variety of problems, as a result I think I will continue to recommend Tubifex.
The real worm to try
Tubifex is a relatively common live, frozen and freeze dried food available. Unlike bloodworm it’s an annelid, true worm and is fully aquatic. It lacks the thick chitin casing of bloodworms, making them much more easy to digest. To cultivate they are less tricky given their lifestyle but do need a constant flow of freshwater.
Unlike bloodworm, Tubifex was vilified for years, this amazing genus is extremely adaptable. This adaptability has meant that Tubifex can be found in the most hostile and polluted habitats and at one time this is where they were collected for the aquarium trade. Due to being collected from very polluted habitats it was not the most ideal live food to avoid pollution. Frozen will be another story as most are gamma irradiated, killing most bacteria on them. But for many years Tubifex is farmed in a clean and sustainable matter.
Unlike bloodworm Tubifex is very high in nutrition (Herawati et al., 2016) and has shown to increase growth when mixed with a prepared diet (Alam et al., 2021) even when compared to other live foods (Mellisa et al., 2018).
Human health
Bloodworm is a known allergen leading to asthma (Wu et al., 2005; Nandi et al., 2014). As someone who is not a medical practitioner I cannot offer much advice, allergies can occur at any time and it is good to be cautious. When dealing with bloodworm, handling particularly wearing disposable gloves can be a good idea, using a tub to defrost it in. It does beg the question given it is quite a common allergen whether to use it at all? In my experience I have met very few people who are allergic to bloodworm.
References:
Alam, M. A., Khan, M. A., Sarower-e-Mahfuj, M. D., Ara, Y., Parvez, I., & Amin, M. N. (2021). A model for tubificid worm (Tubifex tubifex) production and its effect on growth of three selected ornamental fish. Bangladesh Journal of Fisheries, 33(2), 205-214.
Crampton, W. G. (2008). Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae). Neotropical Ichthyology, 6, 599-612.
Delariva, R. L., & Agostinho, A. A. (2001). Relationship between morphology and diets of six neotropical loricariids. Journal of Fish biology, 58(3), 832-847.
Hao, Q., Teame, T., Wu, X., Ding, Q., Ran, C., Yang, Y., … & Zhou, Z. (2021). Influence of diet shift from bloodworm to formulated feed on growth performance, gut microbiota structure and function in early juvenile stages of hybrid sturgeon (Acipenser baerii× Acipenser schrenckii). Aquaculture, 533, 736165.
Herawati, V. E., Nugroho, R. A., Hutabarat, J., & Karnaradjasa, O. (2016). Profile of amino acids, fatty acids, proximate composition and growth performance of Tubifex tubifex culture with different animal wastes and probiotic bacteria. Aquaculture, Aquarium, Conservation & Legislation, 9(3), 614-622.
Mellisa, S., Rahimi, S. A. E., & Umiati, U. (2018). The effect of different live feeds on the growth and survival of comet goldfish Carrasius auratus auratu larvae. In IOP Conference Series: Earth and Environmental Science (Vol. 216, No. 1, p. 012025). IOP Publishing.
Nandi, S., Aditya, G., Chowdhury, I., Das, A., & Saha, G. K. (2014). Chironomid midges as allergens: evidence from two species from West Bengal, Kolkata, India. Indian Journal of Medical Research, 139(6), 921-926.
Valtierra-Vega, M. T., & Schmitter-Soto, J. J. (2000). Feeding habits of cichlid species (Perciformes: Cichlidae) in Caobas lake, Quintana Roo, Mexico. Revista de Biologia Tropical, 48(2-3), 503-508.
Wu, K. C., Räsänen, K., & Hudson, T. J. (2005). Fishing for allergens: bloodworm-induced asthma. Allergy, Asthma & Clinical Immunology, 1, 1-2.
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.
Fake news was the word of the year for 2017, we are often bombarded by information and it can be very difficult to fact check. Sometimes we just don’t have time to check the information we are given is correct, and other times we are relying on the credential of the writer. The aquarium hobby is no exception with so many different websites and social media platforms all arguing for space and more importantly your trust.
As distrust in authority increases there has never been so much division and this leads into the influences of certain media. Unlike the general hobby there is a strong influence of science, whether the website is actually scientific or not.
This is best discussed in terms of two of the biggest myths that have arisen in the last few years.
How Epistylis ruled the world.
For many years the protozoan whitespot, Ichthyophthirius multifiliis was widely considered the most common parasite on fishes, it is well studied in the scientific literature (Francis-Floyd et al., 2016, 2023) followed by velvet, Oodinium and Piscinoodiniasis. Disease is tricky, unlike identifying animals we don’t necessary have the tools as a hobby for an accurate diagnosis, there are thousands of species to separate.
Realistically these two pathogens are one of many that can appear as spots on the fishes body, generally most treatments will cover them. Although there is suggestion that the formalin based treatments are less effective as I discuss here, maybe this has lead to why people come to think they are not dealing with white spot? Because shouldn’t white spot treatments work for I. multifiliis? In addition there is proven acquired immunity to I. multifiliis (Teixeira Alves and Taylor, 2020) but it doesn’t mean that it is unseen. In fact I have noticed a reduced number personally and online of those spotted parasitic cysts, but that is just experience. To add to the confusion not all of these parasites do appear as spots (Sudhagar et al., 2022; Fig 1). I. multifilliis and Piscinoodiniasis is known to target the gills of fishes.
An infection of Piscinoodinium as featured in: Sudhagar, A., Sundar Raj, N., Mohandas, S. P., Serin, S., Sibi, K. K., Sanil, N. K., & Raja Swaminathan, T. (2022). Outbreak of Parasitic Dinoflagellate Piscinoodinium sp. Infection in an Endangered Fish from India: Arulius Barb (Dawkinsia arulius). Pathogens, 11(11), 1350.
This confusion isn’t aided by nematode cysts looking incredibly similar to I. multifilliis and that used to be quite a common misdiagnosis. Going back to the difficulties in identification, microscopes are very important here as many of these pathogens are really only different to look at under the microscope. Using a microscope is one thing but identifying what you are looking at is another, the koi world seems to have this sorted with pathologists available but it seems to have been a reduced talent within the aquarium hobby. There are very few useful books on pathology still available, most if all will be second hand. Microscopes are really only useful for what can be seen so bacteria and even more viruses are another ball game, requiring expensive technology to identify the pathogen.
So, the story is set for Epistylis. Why Epistylis? We will never know but it is likely a random page that came up and sometimes names stick. Unlike Ichthyophthirius multifiliis, Epistylis is easy to remember. I don’t think the why matters but more that it is there, it’s difficult to work out what website started it.
Figure 2: Whitespot, Ichthyophthirius multifiliis as featured in: Martins, M. L., Cardoso, L., Marchiori, N., & Benites de Pádua, S. (2015). Protozoan infections in farmed fish from Brazil: diagnosis and pathogenesis. Revista Brasileira de Parasitologia Veterinária, 24, 1-20.
It might be that fact checking takes time and we should trust what we read to be true. but Ichthyophthirius multifiliis looks nothing alike Epistylis in any way that can be confused as you can clearly see in figure 2 and 3.
Figure 3: Epistylis as featured in: Martins, M. L., Cardoso, L., Marchiori, N., & Benites de Pádua, S. (2015). Protozoan infections in farmed fish from Brazil: diagnosis and pathogenesis. Revista Brasileira de Parasitologia Veterinária, 24, 1-20.
What is more clear is that Epistylis is almost always present and not always as a pathogen, it can also be asymptomatic (Ksepka et al., 2021). But if symptomatic it is expressed as more of a plaque that could be confused with some of the herpes viruses (Fig 3).
So why are they confused? It has to do with this graph (Fig 4). Firstly ich is referring to Ichthyophthirius multifiliis, that we more then often call whitespot in the UK. No citations are provided so this is not backed up with the identification of Epistylis. So some will say the science is wrong, the issue is that genera are described with set features and if those features don’t match then that is not that species, it would be another. That’s how scientific descriptions work. Epistylis doesn’t display itself as distinct round spots whether rough sized or not (Ksepka et al., 2021; Wu et al., 2021; Valladao et al., 2015). If it was so common and lethal there would be more literature when in reality there isn’t that much comparatively. In my experience as well white spot can kill a fish rapidly, and due to the effect on the gills it is quite taxing on the fish (Martins et al., 2015).
So why this whole essay? To discuss misinformation I must first state why this myth isn’t true. Interestingly it is a brilliant story regarding understanding critical analysis.
How to identify a reliable website:
Ability to cite their sources, ideally papers if they are scientists.
Using standard length, just because there are no reliable measurements of total size including the caudal/tail fin.
Avoiding plagiarism, if a scientist this is a key issue.
References:
Francis-Floyd, R., Yanong, R., & Pouder, D. (2023). Ichthyophthirius multifiliis (white spot) infections in fish.
Francis-Floyd, R., Yanong, R., & Pouder, D. (2016). Ichthyophthirius multifiliis (White Spot) Infections in Fish: CIR920/FA006, rev. 12/2016. EDIS, 2016(10).
Ksepka, S. P., & Bullard, S. A. (2021). Morphology, phylogenetics and pathology of “red sore disease”(coinfection by Epistylis cf. wuhanensis and Aeromonas hydrophila) on sportfishes from reservoirs in the South‐Eastern United States. Journal of Fish Diseases, 44(5), 541-551.
Martins, M. L., Cardoso, L., Marchiori, N., & Benites de Pádua, S. (2015). Protozoan infections in farmed fish from Brazil: diagnosis and pathogenesis. Revista Brasileira de Parasitologia Veterinária, 24, 1-20.
Sudhagar, A., Sundar Raj, N., Mohandas, S. P., Serin, S., Sibi, K. K., Sanil, N. K., & Raja Swaminathan, T. (2022). Outbreak of Parasitic Dinoflagellate Piscinoodinium sp. Infection in an Endangered Fish from India: Arulius Barb (Dawkinsia arulius). Pathogens, 11(11), 1350.
Teixeira Alves, M., & Taylor, N. G. (2020). Models suggest pathogen risks to wild fish can be mitigated by acquired immunity in freshwater aquaculture systems. Scientific Reports, 10(1), 7513.
Valladao, G. M. R., Levy-Pereira, N., Viadanna, P. H. D. O., Gallani, S. U., Farias, T. H. V., & Pilarski, F. (2015). Haematology and histopathology of Nile tilapia parasitised by Epistylis sp., an emerging pathogen in South America. Bulletin of the European Association of Fish Pathologists, 35(1), 14-20.
Wang, Z., Zhou, T., Guo, Q., & Gu, Z. (2017). Description of a new freshwater ciliate Epistylis wuhanensis n. sp.(Ciliophora, Peritrichia) from China, with a focus on phylogenetic relationships within family Epistylididae. Journal of Eukaryotic Microbiology, 64(3), 394-406.
Wu, T., Li, Y., Zhang, T., Hou, J., Mu, C., Warren, A., & Lu, B. (2021). Morphology and molecular phylogeny of three Epistylis species found in freshwater habitats in China, including the description of E. foissneri n. sp.(Ciliophora, Peritrichia). European Journal of Protistology, 78, 125767.
Loricariidae, also known under the common names L numbers, whiptail catfishes and pleco’s are popular fishes within the aquarium trade. Many people will come across the problem in their new fish where they will not eat and in fact they might never eat.
Worming
The first sign might be that the fish might have a concaved stomach and the first solution will be to worm the fish. I doubt this is the usual cause of the concave stomach in Loricariid’s but it is worth crossing out, Loricariids do quite frequently have parasitic worm’s (usually nematodes rather then Annelid’s) in the wild and these will maintain at a low level (Borges et al., 2018). If a fish is stressed such as from import this parasite load can become much higher then a healthy level. So there is logic in worming fishes when they arrive and most stores do this. Most wormers cover different internal parasites but the most common would be containing praziquantel, levamisole and flubendazole (do not use with stingrays). I would personally advise definitely not using more then one as they do all have side effects. Generally wormers need to be repeated after a week to cover the parasites lifecycle.
Panaqolus aff. maccus
The importance of getting the fish feeding.
While a rounded and healthy diet is important for wild caught fishes particularly they do need to feed. It is quite a large jump for many from a wild diet to a captive diet and many might not even identify it as food.
More importantly it is possible that the gut flora, microbes will start to decline in number while they are not eating and for shipping this is useful but not for keeping the fish. One possible thing that could help this is rather then adding them to a clean quarantine tank is to one where other similar species have lived, there is likely a benefit from those fishes waste in rebuilding that gut flora lost after shipping.
What should I feed my fish?
First identify what they eat, so their natural diet. While most diets contain the steryotypical fish/insect/krill meal, cereal, vegetable and minimal algae diets this is no issue in the short term but many wont touch these diets at first. So regardless of long term them being vastly different from their natural diet and homogenous whether you have a Trophius, Loricariid or angelfish they actually are the same (Vucko et al., 2017); they can also be unhelpful.
This is important as feeding an incorrect diet can lead to bloat and other issues, it has been commonly noted when Hypancistrus are fed a wholly carnivorous diet.
Carnivorous species
This is only for true carnivores but aspects of this can be fed to others in small numbers with care, avoid it with some of the more extreme algivores such as Ancistrus, Chaetostoma, Baryancistrus etc.
Mussels and prawns are very good for getting a fish feeding at first but the issue with these two food items at high in thiaminase and therefore degrade thiamin, vitamin b1.
Generally for this reason I’d advise a range of frozen foods and for some larger species earthworms might not be a bad choice.
Nannopotopoma sp. ‘Peru/robocop’ at Maidenhead Aquatics at Ascot
Algivores and Detritivores
This includes most Loricariids that people keep to some degree but the specialities within their diet are best looking at later.
These are definitely the most tricky to get feeding at first and I often give a range of options even at the same time. Generally I’d offer that dry/gel diet once or twice a day and vegetables replaced every 12-24 hours depending on how quickly they are braking down.
For dry/gel diets I’d offer certainly Repashy soilent green if possible as I’ve never had a fish fail to give it a go. Later on I’d bulk it out with other ingredients such as algal powders, you could do similar with other gel diets but I can’t say fishes are going to take up them as well. At the end of the day whatever they are eating in the short term is worth it. Remember vegetables and similar are more treats as do not even closely replicate their wild diets.
Vegetables and other easy food items you can leave in for the fishes:
Courgette
Reasonable in nutrition, is willingly eaten by many fishes but they might select either the flesh or skin over the other.
Cucumber
While often declared as low nutrients due to water content they do contain minerals and other compounds that have nutritional value.
Mushrooms (Edible species from supermarket)
Could be part of a staple diet for Panaqolus, Panaque and Hypostomus cochliodon group as they do feed on fungi in the wild (Lujan et al., 2011). It is difficult to say the nutrition levels for these fishes as many might be able to digest more so then nutritional estimates for humans. So far mushrooms are shown to increase weight gain opposed to traditional diets (Zakaria et al., 2021; Dawood et al., 2010), a potential prebiotic (Chandra & Qureshi, 2023) and other potential benefits (Sánchez-Velázquez et al., 2014)
Sweet Potatoes
These doesn’t need to be blanched and I am not convinced by their digestibility for Loricariids (Omoregie et al., 2009) but if they can get the fish feeding that is what matters.
Further on I find whether fishes feed on these more hit and miss.
Green beans
The common bristlenose, Ancistrus sp. is meant to be a big fan of this. Nutrition doesn’t need to be debated but as a plant would be more of a treat after acclimation.
Bell peppers
I don’t think it entirely matters whether the pepper is red, yellow or green but the sugar and nutrition levels will vary.
Pumpkins and other squashes
I find very hit or miss but never blanched them. They can break down very quickly producing a film over the fruit. I would say they are much more similar to courgette.
Later on and narrowing down the diet
While whatever they will eat is generally the best rule as they are acclimatizing over the first few weeks and months. Afterwards I would look to narrowing down their diet to what they would feed on in the wild as in the articles mentioned earlier on.
Is the setup right?
This sometimes get’s forgotten but a major part of why a fish might not be feeding could be they are not getting to the food. Loricariids are slow to feed, some might take hours even without lights to feed and this can make some tankmates ill-suited. Some tankmates might work better where if needed you can remove them to another tank so that is worth considering particularly for many cichlids, many shoaling species in very high numbers or quite a few live numbers.
Planiloricaria cryptodon at Maidenhead Aquatics at Ascot.
References:
Borges, W. F., de Oliveira, M. S. B., Santos, G. G., & Tavares-Dias, M. (2018). Parasites in Loricariidae from Brazil: checklist and new records for fish from the Brazilian Amazon. Acta Scientiarum. Biological Sciences, 40, 1-9.
Chandra, O. P., & Qureshi, Y. (2023). Importance of mushroom supplementation as a prebiotic amalgamation in fed diet of improvement of weight gain (WG) in Nile Tilapia,(Oreochromis niloticus). Journal of Pharmaceutical Negative Results, 1681-1687.
Dawood, M. A., Eweedah, N. M., El-Sharawy, M. E., Awad, S. S., Van Doan, H., & Paray, B. A. (2020). Dietary white button mushroom improved the growth, immunity, antioxidative status and resistance against heat stress in Nile tilapia (Oreochromis niloticus). Aquaculture, 523, 735229.
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.
Omoregie, E., Igoche, L., Ojobe, T. O., Absalom, K. V., & Onusiriuka, B. C. (2009). Effect of varying levels of sweet potato (Ipomea Batatas) peels on growth, feed utilization and some biochemical responses of the cichlid (Oreochromis Niloticus). African Journal of Food, Agriculture, Nutrition and Development, 9(2), 700-712.
Sánchez-Velázquez, J., Peña-Herrejón, G. A., & Aguirre-Becerra, H. (2024). Fish Responses to Alternative Feeding Ingredients under Abiotic Chronic Stress. Animals, 14(5), 765.
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.
Zakaria, Z., Abd Rasib, N. A., & Tompang, M. F. (2021). Spent mushroom substrate based fish feed affects the growth of catfish (Clarias gariepinus). In IOP Conference Series: Earth and Environmental Science (Vol. 765, No. 1, p. 012082). IOP Publishing.
Corydoras is a genus of Catfishes in the family Callichthyidae. Callichthyidae includes: Callichthyinae (Callichthys, Lepthoplosternum, Hoplosternum, Megalechis and Dianema); Corydoralinae which is the focus of this article and revision. Figure 1 explains the topography (family tree format) of this group but bare in mind it doesn’t reflect the current knowledge for Corydoralinae.
Figure 1: Phylogeny of Callichthyidae. Bare in mind the topography (shape) of Corydoras doesn’t match our current understanding. As featured in: Shimabukuro-Dias, C. K., Oliveira, C., Reis, R. E., & Foresti, F. (2004). Molecular phylogeny of the armored catfish family Callichthyidae (Ostariophysi, Siluriformes). Molecular Phylogenetics and Evolution, 32(1), 152-163.
Previously many genera were inferred for members of what was known for a long time as Corydoras but over time these were synonymized finalizing with Britto (2003) which resulted in Brochis no longer being valid. To put it simply as there were many reasons behind but also to have Corydoras as the genus it was then Brochis would have to be Corydoras.
Figure 2: Phylogeny of Corydoralinae featured in: Alexandrou, M. A., Oliveira, C., Maillard, M., McGill, R. A., Newton, J., Creer, S., & Taylor, M. I. (2011). Competition and phylogeny determine community structure in Müllerian co-mimics. Nature, 469(7328), 84-88.
The history is a bit messy. We have known for a long time Corydoras has had a lineage system, this was explained clearly in Alexandrou et al (2011). This phylogeny shows how embedded Brochis is inside of Corydoras and therefore would not easily be valid as a genus.
The issue of type species
So while many of the ‘Corydoras‘ kept in the aquarium trade are not Corydoras, the type, C. geoffroy places in lineage 1. These would be the only true Corydoras, basically this is the reference species in a way.
Some might note what was known as Aspidoradini, a tribe separate to what was Corydoras branches out in the middle of Corydoras, more problems. It’s really messy.
What are the new genera?
Corydoras: Used to represent lineage 1 of Corydoras. These have a but curved block shaped head, most distinctively is a filament behind the barbel’s which can look like an additional barbel.
Aspidoras: Always known as Aspidoras but excludes Gastrodermis pauciradiatus.
Scleromystax: Sometimes known as bearded Corydoras, the only to show really clear sexual dimorphism through odontodes.
Gastrodermus: Originally the C. elegans group, lineage 5 and the microcorydoras such as G. pygmeaus and G. hastatus. Much shorter and rounder in the head but still slightly trinagular unlike Hoplisoma.
Osteogaster: Originally the C. aeneus group, contains the bronze, O. aeneus. Rounded head, short.
Brochis: This is a much larger group, likely for the time being. Contains the whole of lineage 8 from what was Brochis to species such as C. arcuatus. Similar to Corydoras the majority have large heads but these lack the curvature of Corydoras, similarly contains many large members.
Hoplisoma: Lineage 9, another very popular genus from the trade. Very rounded head but much shorter then Osteogaster.
Corydoradinae head shapes
The clearest way to see the difference between the different genera is their head shapes, there is quite the diversity as shown in the above figure. The majority of these genera can be identified from that head shape in my opinion. Brochis seems to display the widest range of morphological disparity in head shape but this can be expected from such a large genus.
Why is this revision important?
This revision reflects our current knowledge of the group Corydoradinae, both regarding morphological and molecular information. Rather then have one large category which doesn’t describe the morphological diversity or any phylogenetic information, these genera are easier to navigate particularly for a hobbyist. Not just does their morphology differ but likely their care. I already know Corydoras and some Brochis display territorial behavior which is not reflective of all groups, from a hobbyist view point knowing the genera helps avoid this, or avoid larger species.
Revisions are normal in science as technology and knowledge advances, they aren’t done for no reason or for publication. Over time we have developed techniques that have helped us understand the evolution of fishes better and therefore give them more accurate names that reflect this evolution. Technology such as Computerized tomography (CT) scanning, extracting DNA from formalin preserved/historical specimens, gene expression, developmental techniques etc. We can now understand fishes in a way we never could before, it means that change is inevitable but it’s the path to understanding evolution, biodiversity and reflecting that in how we name species, genera, families etc.
This work was done by the scientists; Angelica C. Dias, Luiz F. C. Tencatt, Fabio F. Roxo, Gabriel de Souza da Costa Silva, Sérgio A. Santos, Marcelo R. Britto, Dr. Martin I. Taylor and Dr. Claudio Oliveira.
No doubt our knowledge of Corydoradinae wouldn’t be the same without the efforts of Steven Grant (Catfishes of the World) and Ian Fuller who runs Corydoras World, both have done a lot for bridging the gap between the hobbyist and the scientist. Corydoras World I can certainly recommend for anyone who wants to learn more about this curious group of fishes.
What species are what?
To save time I wont cite authors, but this should ideally be done. I wont include C and CW numbers as it’ll make the lists much much longer.
Corydoras
Corydoras acutus
Corydoras amapaensis
Corydoras areio
Corydoras aurofrenatus
Corydoras blochi
Corydoras caramater
Corydoras cervinus
Corydoras coriatae
Corydoras cortesi
Corydoras desana
Corydoras filamentosus
Corydoras fowleri
Corydoras fulleri
Corydoras geoffroy
Corydoras maculifer
Corydoras narcissus
Corydoras negro
Corydoras ourastigma
Corydoras oxyrhynchus
Corydoras pastazensis
Corydoras saramaccensis
Corydoras sarareensis
Corydoras semiaquilus
Corydoras septentrionalis
Corydoras serratus
Corydoras simulatus
Corydoras solox
Corydoras spilurus
Corydoras stenocephalus
Corydoras treitlii
Corydoras vittatus
Corydoras zawadzkii
Aspidoras
Aspidoras albater
Aspidoras aldebaran
Aspidoras azaghal
Aspidoras belenos
Aspidoras brunneus
Aspidoras carvalhoi
Aspidoras depinnai
Aspidoras fuscoguttatus
Aspidoras gabrieli
Aspidoras kiriri
Aspidoras lakoi
Aspidoras maculosus
Aspidoras mephisto
Aspidoras poecilus
Aspidoras psammatides
Aspidoras raimundi
Aspidoras rochai
Aspidoras velites
Scleromystax
Scleromystax barbatus
Corydoras lacerdai
Scleromystax macropterus
Scleromystax prionotos
Scleromystax reisi
Scleromystax salmacis
Scleromystax virgulatus
Gastrodermus
Gastrodermus bilineatus
Gastrodermus elegans
Gastrodermus gracilis
Gastrodermus guapore
Gastrodermus hastatus
Gastrodermus latus
Gastrodermus mamore
Gastrodermus nanus
Gastrodermus napoensis
Gastrodermus nijsseni
Gastrodermus paucerna
Gastrodermus pauciradiatus
Gastrodermus pygmaeus
Gastrodermus undulatus
Osteogaster
Osteogaster aeneus
Osteogaster eques
Osteogaster hephaestus
Osteogaster maclurei
Osteogaster melanotaenia
Osteogaster rabauti
Osteogaster zygatus
Brochis
Brochis agassizii
Brochis amandajanea
Brochis ambiacus
Brochis approuaguensis
Brochis arcuatus
Brochis bethanae
Brochis bifasciatus
Brochis britskii
Brochis brittoi
Brochis condiscipulus
Brochis costai
Brochis crimmeni
Brochis crypticus
Brochis delphax
Brochis deweyeri
Brochis difluviatilis
Brochis ephippifer
Brochis garbei
Brochis geryi
Brochis gomezi
Brochis haraldschultzi
Brochis heteromorphus
Brochis imitator
Brochis incolicana
Brochis isbrueckeri
Brochis lamberti
Brochis leopardus
Brochis multiradiatus
Brochis noelkempffi
Brochis ornatus
Brochis orphnopterus
Brochis pantanalensis
Brochis pinheiroi
Brochis pulcher
Brochis reticulatus
Brochis robineae
Brochis robustus
Brochis seussi
Brochis sodalis
Brochis spectabilis
Brochis splendens
Brochis sychri
Brochis virginiae
Hoplisoma
Hoplisoma acrensis
Hoplisoma adolfoi
Hoplisoma albolineatum
Hoplisoma amphibelum
Hoplisoma apiaka
Hoplisoma araguaiaensis
Hoplisoma armatum
Hoplisoma atropersonatum
Hoplisoma axelrodi
Hoplisoma baderi
Hoplisoma benattii
Hoplisoma bicolor
Hoplisoma boehlkei
Hoplisoma boesemani
Hoplisoma bondi
Hoplisoma breei
Hoplisoma brevirostris
Hoplisoma burgessi
Hoplisoma carlae
Hoplisoma caudimaculatum
Hoplisoma cochui
Hoplisoma colossus
Hoplisoma concolor
Hoplisoma copei
Hoplisoma coppenamensis
Hoplisoma cruziensis
Hoplisoma davidsandsi
Hoplisoma diphyes
Hoplisoma duplicareum
Hoplisoma ehrhardti
Hoplisoma esperanzae
Hoplisoma evelynae
Hoplisoma eversi
Hoplisoma flaveolum
Hoplisoma froehlichi
Hoplisoma gladysae
Hoplisoma gossei
Hoplisoma granti
Hoplisoma griseum
Hoplisoma gryphus
Hoplisoma guianensis
Hoplisoma habrosum
Hoplisoma julii
Hoplisoma kanei
Hoplisoma knaacki
Hoplisoma lacrimostigmata
Hoplisoma leucomelas
Hoplisoma longipinnis
Hoplisoma loretoensis
Hoplisoma loxozonum
Hoplisoma lymnades
Hoplisoma melanistium
Hoplisoma melini
Hoplisoma metae
Hoplisoma micracanthus
Hoplisoma microcephalum
Hoplisoma multimaculatum
Hoplisoma nattereri
Hoplisoma oiapoquensis
Hoplisoma ortegai
Hoplisoma osteocarum
Hoplisoma paleatus
Hoplisoma panda
Hoplisoma paragua
Hoplisoma parallelum
Hoplisoma pavanelliae
Hoplisoma petracinii
Hoplisoma polystictum
Hoplisoma potaroensis
Hoplisoma punctatum
Hoplisoma revelatum
Hoplisoma reynoldsi
Hoplisoma sanchesi
Hoplisoma schwartzi
Hoplisoma similis
Hoplisoma sipaliwini
Hoplisoma steindachneri
Hoplisoma sterbai
Hoplisoma surinamensis
Hoplisoma trilineatum
Hoplisoma tukano
Hoplisoma urucu
Hoplisoma weitzmani
Hoplisoma xinguensis
References:
Alexandrou, M. A., Oliveira, C., Maillard, M., McGill, R. A., Newton, J., Creer, S., & Taylor, M. I. (2011). Competition and phylogeny determine community structure in Müllerian co-mimics. Nature, 469(7328), 84-88.
Britto, M. R. (2003). Phylogeny of the subfamily Corydoradinae Hoedeman, 1952 (Siluriformes: Callichthyidae), with a definition of its genera. Proceedings of the Academy of Natural Sciences of Philadelphia, 153(1), 119-154.
Dias, A. C., Tencatt, L. F., Roxo, F. F., Silva, G. D. S. D. C., Santos, S. A., Britto, M. R., … & Oliveira, C. (2024). Phylogenomic analyses in the complex Neotropical subfamily Corydoradinae (Siluriformes: Callichthyidae) with a new classification based on morphological and molecular data. Zoological Journal of the Linnean Society, zlae053.
Shimabukuro-Dias, C. K., Oliveira, C., Reis, R. E., & Foresti, F. (2004). Molecular phylogeny of the armored catfish family Callichthyidae (Ostariophysi, Siluriformes). Molecular Phylogenetics and Evolution, 32(1), 152-163.
Little seems known about the diet of Corydoradinae, it might be due to a generalization of the genus but also a lack of understanding of their ecology. For scientists it is a relatively small genus from a small family, Callichthyidae which also contains genera such as Megalechis, Hoplosternum and Aspidoras.
Brochis bethanae CW006 also known as the Narcisso Corydoras taken at Maidenhead Aquatics, Ascot
There is no doubt that Corydoras feeds largely as a carnivore but as a term that is very vague. These fishes are hardly hunting down capybara that enter the water or swarming round the carcasses of fishes. Carnivory purely just refers to the fact an animal eats an animal, and what is defined as an animal is just Animalia which is a gigantic category of organisms. Animalia covers from the simple sponges and corals all the way to molluscs, mammals and fishes, it includes some strange organisms as well like bryozoa and jellyfish. Each of these animals will have different nutritional compositions, some toxins but also accessibility. It is well known that insectivores (carnivores that specialize on insects) are not able to access nutrition from fishes, mammals etc. efficiently (Žák et al., 2022), this also increases nitrogenous waste. There might be other aspects of nutrition commonly missed such as perhaps the importance of chitin? It’s very difficult to digest, too much and the food item wont be processed, too little might result in blockages. It reminds me very much of the bloodworm used in the aquarium trade having a strong chitin casing compared to the chromatid larvae the fishes are likely eating in the wild. I have seen bloodworm pass out the fish as if it hadn’t been eaten at all, even carnivorous fishes. Not just does carnivory cover a wide range of different nutritional profiles and species but also modes of feeding. It is very different to catch and feed on a whole fish as it is to maybe feed on scales (lepidophagy), break down snails (durophagy), maybe extract a snail from it’s shell etc. Carnivory is so obviously diverse compared to herbivory but it still is best visualized like a field of grass, all grass specialists but put sheep, cattle and horses out and they will all feed on very different parts of the grass.
What I am emphasizing is not to generalize any dietary category and just fall to the general diets for fishes. Carnivory is just a man made category regardless and doesn’t reflect realistically aquatic dietary niches.
Corydoradinae has previously been identified as an omnivore by Nijssen (1970) although only used aquarium fishes as evidence. This paper records them feeding on fallen leaves of which I find particularly strange. Although a particular fondness for invertebrates is noted, particularly tubifex and daphina, identifying the worms using their highly evolved sense of smell/taste. This record is later referenced in Alexandrou et al. (2011) but also noted that they feed on algae, insects, zooplankton and annelids. Algae I would not be surprised that is consumed but I do not believe they are targeting it, much like invertebrates are found in small numbers the guts of grazing Loricariids.
Isotope analysis was used to compare different lineages of Corydoras and identify any partitioning in where and what they feed on. Different lineages display divergent nutritional profiles between different genera of Corydoradinae based on head shape, eye placement and body depth. There is a clear difference between the diet of the longer snouted and shorter snouted Hoplisoma and Gastrodermus, I can assume due to the depths of substrate that can be exploited by either. These longer snouted, Corydoras are referenced as feeding on a lower trophic level (Alexandrou et al., 2011). This could infer on feeding on more algaes but maybe those lower trophic level invertebrates such as worms who would be lower down in the substrate then predatory invertebrates.
The shorter to medium snouted Hoplisoma paleatum, the peppered ‘Corydoras‘ is recorded as feeding largely on fly larvae such as chromatid’s with a small addition of nematode’s. Algae and plant fragments are recorded in the gut but near minimal volumes, less then substrate ingested (Bertora et al., 2021).
So the picture of what Corydoradinae eat in the wild is unclear.
The Dietary Morphology of Corydoras
Figure 1: Hoplisoma trilineatum skeletal anatomy produced by computerized tomography (CT) scanning. Produced by: Lowe, A., Summers, A. P., Walter, R. P., Walker, S., & Paig-Tran, E. M. (2021). Scale performance and composition in a small Amazonian armored catfish, Corydoras trilineatus. Acta Biomaterialia, 121, 359-370.
Again, an unclear topic. We know Corydoradinae have oral jaws (Fig 1) at the front of the head humongous with our the general vertebrate jaw. These oral jaws contain teeth (Huysentruyt et al., 2011) but there seems to have been no exploration of the diversity of these teeth. These oral jaws are very similar to other invertivores (feeds on invertebrates), being elongate to extract food items out of crevices or the substrate.
What is not researched is the secondary pair of jaws found in most fishes, the pharyngeal jaws. While the oral jaws in fishes are often involved in prey capture, the pharyngeal jaws are involved in prey processing, so the grinding and breaking down. These are at the back of the mouth so aren’t obvious but when you see a fishes head move after feeding it’s likely those jaws are moving. Corydoradinae do have pharyngeal jaws, they contain teeth (Huysentruyt et al., 2011) but we have no idea how this morphology differs across Corydoradinae. In Osteogaster aenea Huysentruyt et al. (2011) identified elongate pharyngeal teeth which would confirm that at least O. aeneus is not evolved to feed on snails but the jaws do seem some what robust. It contrasts from those species that feed on algae to any extent who seem to have much more simplistic and often bladed pharyngeal anatomy. Most research into pharyngeal anatomy focuses on cichlids of which might not be the best reference given differential feeding behaviour.
Head shape can tell a lot about the fish, these fishes have such inferiorly facing mouths will be feeding around the substrate. What is more interesting is the shape of the snout mentioned earlier but we know so little about it. Those elongate snouts certainly allow the fish to dig deeper for food but how it effects them we only have clues.
What should I feed my Corydoras?
These are certainly not feeding on fishes, there is also the misconception that because fishes die that all fishes have access to them. Generally weaker individuals would be picked up by predators before they die and any dead fish would be more quickly exploited by species evolved to detect and quickly feed on carcasses. So fish meal is logically best avoided. These fishes also do not feed on plants so cereals are certainly of little use. This means those general diets are not great for them, most containing fish meal, cereals, vegetables etc. usually in that order.
Luckily for carnivores there is a few options for insect based foods. Fish Science is generally good and they offer some diversity. Fluval bug bites can be okay but still has quite a lot of fish meal and cereals in it. Repashy bottom scratcher is certainly worth looking at, being a gel diet you can add additional ingredients to it. I wouldn’t be afraid to use either Fish Science or Repashy bottom scratcher as the basis of the diet then frozen and freeze dried foods to build on it creating a more well rounded diet. Certainly live foods are worth looking at and would offer a lot of enrichment.
Corydoradinae are very forgiving regarding diets so experimenting is certainly possible.
Frozen foods are great but often will not contain all of the nutrition a species might require. In the wild most fishes will feed on hundreds of species and the narrow range of frozen foods available likely doesn’t compare nutritionally. These are great as enrichment or an addition to a fishes diet but not as a complete diet.
Protein Blisters
This is something that will always need mentioning regarding diets. I am not convinced it is caused by too much protein, even protein that isn’t absorbed/taken up by the fish e.g. excreted as nitrogenous waste. There is no evidence either way, it is clear bacteria can cause blisters and cysts but it can’t be said every cyst is caused by them without exploring further. Some frozen/live foods such as bloodworm can harbor Aeromonas (Senderovich et al., 2008) so it is difficult to make assumptions but there is little research on that.
A suggestion has been a form of gas bubble disease, true gas bubble disease as I call it though is caused from supersaturation of gases in the water, or some change in pressure resulting in bubbles forming in tissues very rapidly like the bends. It kills extremely rapidly as those bubbles form and burst blood vessels. There are other similar diseases like I have seen extreme algae growth associated, not proven though, to cause bubbles in some fishes but doesn’t kill and they are very localized.
We see similar in Loricariids, also armored and personally I would associate it with an infection of some kind. Blisters are tricky though as it’s such a general pathological symptom it could mean anything.
References:
Alexandrou, M. A., Oliveira, C., Maillard, M., McGill, R. A., Newton, J., Creer, S., & Taylor, M. I. (2011). Competition and phylogeny determine community structure in Müllerian co-mimics. Nature, 469(7328), 84-88.
Bertora, A., Fontanarrosa, M. S., Grosman, F., Sanzano, P., & Rosso, J. J. (2021). Trophic ecology of the Neotropical tolerant fish Corydoras paleatus under the influence of contrasting environmental conditions in a prairie stream. Anais da Academia Brasileira de Ciências, 93, e20200981.
Huysentruyt, F., Geerinckx, T., Brunain, M., & Adriaens, D. (2011). Development of the osteocranium in Corydoras aeneus (Gill, 1858) Callichthyidae, Siluriformes. Journal of Morphology, 272(5), 573-582.
Lowe, A., Summers, A. P., Walter, R. P., Walker, S., & Paig-Tran, E. M. (2021). Scale performance and composition in a small Amazonian armored catfish, Corydoras trilineatus. Acta Biomaterialia, 121, 359-370.
Nijssen, H. (1970). Revision of the Surinam catfishes of the genus Corydoras Lacépède, 1803 (Pisces, Siluriformes, Callichthyidae). Beaufortia, 18(230), 1-75.
Senderovich, Y., Gershtein, Y., Halewa, E., & Halpern, M. (2008). Vibrio cholerae and Aeromonas: do they share a mutual host?. The ISME journal, 2(3), 276-283.
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.
Banjo catfishes, Aspredinidae are a frequent catfish family that appears within the aquarium hobby although the majority will have seen and kept individuals from a single genus, Bunocephalus. Little seems known about the other Aspredinidae that rarely circulate the hobby.
Taxonomy and Phylogenetics
Aspredinidae is comprised of 13 genera and 49 species (Fricke et al., 2024), so it is a relatively small group of catfishes. As above Bunocephalus is the most commonly seen genus although Platystacus cotylephorus, Pterobunocephalus, Pseudobunocephalus and Amaralia are seen in the trade. The majority of these represent the smaller members of the family growing to around a maximum of 6-7cm SL, although Platystacus cotylephorus being the exception growing closer to 30cm SL similar to it’s sister genus, Aspredo (Carvalho et al., 2018; Fig 1). At one point Platystacus cotlyphorus was actually placed in Aspredo and you might see that in museum collections. I am unclear as to whether Aspredo does enter the aquarium trade.
Figure 1: The phylogenetic relationships of Aspredinidae by Carvalho et al. (2018): Carvalho, T. P., Arce, M., Reis, R. E., & Sabaj, M. H. (2018). Molecular phylogeny of Banjo catfishes (Ostaryophisi: Siluriformes: Aspredinidae): A continental radiation in South American freshwaters. Molecular Phylogenetics and Evolution, 127, 459-467.
Between these groups there is a clear morphological trend, although identification to species level in some can be particularly tricky.
This group is exclusive to South America but particularly widespread, curiously much of their morphology seems conserved across the group and given the limited species number it infers to me they are quite generalist and adaptable. The adaptability is certainly evident for anyone who has kept Bunocephalus.
Figure 2: Pterobuncephalus sp. ‘Peru white’.
Platystacus cotylephorus is one of the most elongate members of the family, it has a large caudal peduncle with an elongate anal fin. This anal fin extending from the anus to close to the caudal fin is rather distinctive but is also found in Aspredo aspredo. In my experience, it seems to help with swimming in the water column and frequent activity, something I also saw in Pterobunocephalus sp. ‘Peru white’ (Fig 2). Unlike Bunocephalus these fishes are a lot more ventrally-dorsally compressed. Their pectoral fin spines are much stronger and more heavily serrated.
These are largely bottom dwelling fishes with inferior mouths, facing downwards and that is largely where they feed. Don’t be mistaken Platystacus will enter the water column occasionally, I find mostly when introduced to a new tank, they seem to exploit the current but unlike a typical fish are not the best at directing themselves. They use their larger pectorals and pelvic fins to glide with the anal fin like a stern to help guide themselves. When moving around the bottom they use that anal fin and eel shape much more. I can imagine in the wild they are much more adapted to leaf litter.
Many species of Aspredinidae display a wide diversity of colouration within species and it doesn’t seem to be due to locality. Platystacus cotylephorus being no exception but generally there are lighter more beige individuals and darker mahogany wood individuals, some have more markings then others.
Strangely there is little literature on the species regardless of it’s fascinating biology.
Etymology
Platys refers to the flat shape at the anterior of the fish and acus refers to the needle like posterior of the fish. Cotylephorus is even more interesting cotyla refers to a cup and phorus to bear. This scientific name is perfect, it describes the shape of the fish, the species epithet meaning bearing cups, these fishes have eggs attached via stalks to the abdomen of the fish (https://etyfish.org/siluriformes10/).
Diet
These are carnivores, pretty clear likely carnivores given their morphology, they do seem to lack oral teeth although I would not be surprised if they had substantial pharyngeal jaws. They respond with a reasonable speed to any of those invertebrate based food items and do not seem fussy.
The main issue with Platystacuscotylephorus and this goes for other Aspredinidae it seems that their abdominal cavity is much more restricted then Bunocephalus or in fact other catfishes. They cannot handle certain food items or high volumes, it seems to cause bloat that can be fatal. This means they really shouldn’t be in a tank where they can gorge themselves to death but also be careful to avoid too much fish meal based diets. I keep mine with Baryancistrus spp. right now which means I can control how much they have while the Baryancistrus have an awful lot of algaes.
So while for carnivorous fish I think there is a whole range they can be fed, for Platystacus cotylephorus I’d step back and think. If that abdomen is extended and the females do produce a lot of eggs, then it is best to reduce feeding for the time being.
Vocalization through stridulating
I’m surprised this isn’t talked about as much in the hobby. Many Aspredinidae or catfishes in general are capable of making sounds, sometimes it’s from the swim bladder but in this case it’s from those pectoral fins. Platystacus cotylephorus seem to make a range of sounds but it’s difficult to know what they are for. If handled and usually before they draw blood there is a higher pitch sound. I have caught a male during water being emptied for a water change making a cracking/clapping like sound, a much lower pitch sound.
Sounds aren’t frequently heard but it does happen.
Shedding skin
I’m not sure how clear it is as to why they do this, it is probably and possibly to a source of irritation. Unlike many other fishes it is not just the slime coat but a thin layer of skins. I find sometimes it seems to be done frequently but all I can say is these fishes are capable of doing it.
Sexing
This is assumed by the dorsal fin, males having dorsal extensions that can develop rapidly while the fish matures. Females have a much more rounded dorsal fin. Other then that I certainly would say there is little other difference unless that female is full of eggs and can have a slight yellow tinge to the abdomen.
Spawning
As far as I know Platystacus cotylephorus has never been spawned in captivity. Females carry the eggs on stalks on their abdomens and individuals have been imported in this state. It is not just Platystacus who does this but many members of Aspredinidae. These stalks don’t just function as attachment but somewhat function as a placenta for the developing embryo’s (Wetzel et al., 1997). I would be curious if there is any correlation between activity levels and this reproductive method between species.
Water Parameters and Habitat
A curious ability of this species is it’s range of habitats, while originating from Brazil they are capable of moving from fresh to brackish and even identified in marine waters. Could this be why they can shed their skin? But it makes them perfectly adaptable. I have been curious in the past that they need these changes to survive but it seems currently that isn’t true and the main reason they seem to fail in captivity is diet.
Photos of these fishes in the wild show them moving across very varied substrates, they do have some capability to dig in the sand and therefore I’d certainly provide that. I so suspect they are adapted to leaf litter although I find it a pain to clean around without trapping a lot of waste.
References
Carvalho, T. P., Arce, M., Reis, R. E., & Sabaj, M. H. (2018). Molecular phylogeny of Banjo catfishes (Ostaryophisi: Siluriformes: Aspredinidae): A continental radiation in South American freshwaters. Molecular Phylogenetics and Evolution, 127, 459-467.
Wetzel, J., Wourms, J. P., & Friel, J. (1997). Comparative morphology of cotylephores in Platystacus and Solenostomus: modifications of the integument for egg attachment in skin-brooding fishes. Environmental Biology of Fishes, 50, 13-25.
This is a subject that rarely gets discussed as it’s not something many are taught, even in the scientific community many are not taught it. Two important terms are needed here; Taxonomy, the study involving the description of species, genera and the larger groupings and Nomenclature, this is more about how these species are named. Since the mid-1700’s we have been using a system for scientific names known as Binomial Nomenclature created by Carl Linnaeus (a name everyone should know). This binomal system uses two names, the genus name (E.g. Corydoras) and the species name/epithet (aeneus), together this forms Corydoras aenus.
Pseudohemiodon apithanos at Maidenhead Aquatics at Ascot
Scientific names on the face of them aren’t that complex, and a lot of the rules are for those describing species, some rules are formal and others not. There is a guide, rulebook or bible for the naming of species, genera etc. and this is known as the International Code for Zoological Nomenclature, as the name suggests plants, fungi and bacteria have other codes.
The Groupings
To understand scientific names it can be useful to know the hierarchy of animal groups; Kingdom, Phylum, Class, Order, Family, Genus and finally Species. So an example would be Animalia (animals), Chordata (vertebrates, sea squirts etc.), Actinoptergii (Ray-finned fishes), Siluriforme (Catfishes), Loricariidae (Armoured suckermouth catfishes/plecos), Ancistrus (Bristlemouth catfishes/plecos) and Ancistrus ranunculus. There are some intermediate groups e.g. subfamily so in this case for Ancistrus would be Hypostominae, other genera in that group would be like Hypostomus, Hypancistrus, Scobinancistrus etc. I have been giving common names to some of these groups but beware as they can be misleading e.g. Synbranchiformes are eels but they are not closely related to Anguilliforme eels. Ray finned fishes, Actinopterygii doesn’t mean they all have fins, one that I find confuses students is they are asked to find lobe finned fishes, Sarcopterygii and presented with the African lungfish (Protopterus), or worse humans (Homo sapien). So this goes to show how useful scientific names and the systems are, they do teach placement within a group, or more precisely these groups are known as clades.
So this idea of grouping brings up another study, phylogenetics, unlike the name suggests this study uses morphology/anatomy and/or DNA. It is the study of evolutionary relationships between species to produce beautiful trees that hypothesize how species are related. When you know these relationships between whatever interests you, you can then identify trends and maybe keep species who have little information on them, of course understanding anatomy is important too.
Pangio myersi
Why are Scientific Names Important?
Scientific names are universal, they are the same around the world.
There is documentation e.g. papers which say the characteristics that define each species. So you can use these to identify your species.
Many species lack common names.
They are peer reviewed, other scientists have to agree with the decision.
Common names are deceptive, mountain chicken is not a bird at all and a racoon dog is neither a racoon or dog.
If importing fish the fact scientific names are universal becomes important as they might use direct translations or their own names e.g. Pez globo as common names.
Common names change frequently over time with no ability to record how they change.
Common names can often describe many vastly different species e.g. Snowball pleco covers Hypancistrus spp. and Baryancistrus sp. ‘L142’ so the size difference is a 7-10cm SL fish vs a 25-30cm SL fish with a much more specialized diet.
How to Write Scientific Names
This is the topic that maybe throws the most people.
So lets go with one of my favorite scientific names:
Satanoperca jurupari (Heckel 1840)
Firstly the genus first letter is uppercase, the species is in lower case. This designates the species from the other groupings as the larger groupings above e.g. genus, family etc. are all uppercase for the first letter.
Scientific names, genus and species are in italics. If hand written then the scientific name can be underlined. This designates a scientific name from the common names.
There is no plural or singular to genera or species names. Corydora is not the name of a genus, Corydoras is the singular and the plural.
When first stated technically all scientific names should be cited. This is like if you were citing a paper but it cites the work describing the species, not any revisions just the species. If the name is in brackets it means that there has been a revision in the genus, if not there has been no revision. So in this case Satanoperca jurupari was originally in Geophagus.
Platystacus cotylephorus from Maidenhead Aquatics at Farnham
The Short Hand, and Their Meanings
Frequently you’ll come across letters with a full stop after and they are important. Some designate opinions about a species identification and others just save time.
sp. This means species as singular. Usually used where the species is not known or is undescribed. It will mostly be used where the genus is known but can be used even at the family level. Should not be italicized. E.g. Corydoras sp. one unknown or described species of Corydoras.
spp. This is plural for multiple species. It can be used for unknown or undescribed species but is more often to describe many species in the genus. E.g. Corydoras spp. multiple species of Corydoras.
subsp. Subspecies but most of us don’t really use subspecies, it’ll follow the scientific name between species and subspecies name.
aff. affinity with, means that it is similar to that species but likely not. E.g. Parancistrus aff. aurantiacus, it is similar to Parancistrus aurantiacus but in body shape, size etc. certainly a different species.
cf. confer to, similar to the species listed and likely that species but unsure.
There are a few others but they aren’t quite as important.
Etymology, the best bit!
Etymology is the origin of words, every scientific name will mean something usually a description of anatomy, a location, a person, an animal etc. This makes them so fascinating and unlike common names the original paper will include why the name was chosen and what it means.
So for the species earlier, Satanoperca jurupari. Satan actually refers to demons, this is largely due to these fishes being mouth brooders and locals associating them with eating their children. Demon in many countries refers more to spirit. Perca refers to perch, cichlids are Periformes but generally perch like. So this genus, Satanoperca is the demon perch. Many of the species in this genus are named after demons, S. lilith is another associated with eating children. S. jurupari is no exception but this is a local demon or more spirit who swallows children, I believe it should be pronounced as if you were saying yurupari.
I recommend checking out Etyfish for anyone who is interested in etymology of scientific names.
Scientific Names are not Latin
There is the idea that all scientific names are in Latin, and when you look at the names properly this is clearly untrue, they are not in the Latin language. Almost every language probably has scientific names in that language and they can be a hybrid of the two. Latin and Greek maybe were the most popular for a time period, it might have a social historical reason why but with most of us not being taught Latin in school I think that is changing. From the start species have been named after people whose names were not Latin.
This is why the term Latin names is generally incorrect.
Who are These Species Named After?
Not the author of the species description, ideally. It’s seen as more polite to name it after someone else, it is generally a huge honor to have a species named after you. It is usually a notation of the amount of work someone has done in a field although celebrities, political figures etc. have species named after them. Every scientist has their preferences and sometimes the naming after a well known person is great, needed publicity for scientists, and that can equate to funding or jobs. There is still debate about names that have become questionable.
Some of the best are the number of species named after characters in mythology, books and tv shows. We have quite a few Tolkien fans who study catfish as scientific names show, but there is also Aenigmachanna gollum.
Hoplarchus psittacus at Pier Aquatics, Wigan
Scientific names have a Gender
English is a language that we all know lacks gender, in French and Spanish it is quite clear words are gendered. Scientific names are as well, only those describing the species really have to concern themselves with this but the name can be feminine, masculine or neutral and this can change, a revision of the genus can change the gender. A great example of changing names was Megalechis thorcata was Hoplosternum thoracatum.
The Dreaded Pronunciation
I think it’s only correct if a species is named after someone aiming for a good pronunciation is only polite. Otherwise everyone does pronounce things differently, those aiming for a correct Latin or Greek pronunciation we aren’t entirely sure how they pronounced everything in the past, additionally like the UK and US, pronunciation varied between localities. Some pronunciations are difficult for some people, and that’s fine. Generally I think no one really minds how you pronounce scientific names, there are some strange ones but who knows theirs could be more correct.
Scientific Names Change
This is an argument many will bring up against their use, common names change as well and there is often no record to identify previous names. I grew up knowing the dwarf butterfly cichlid, a beautiful species yet over the years their name changed to the ramirezi cichlid, then ram cichlid but now there are many common names for the same species, Mikrogeophagus ramirezi. German blue ram being one which technically should only refer to a certain line of the fish, 99% of people no doubt have fishes with no connection to this line but entirely farmed in Asia. I have seen many more.
Scientific names do change, they change for good reason, they change as we know more about a species. Species get split up sometimes but they also might move genera. This shouldn’t be seen as a bad thing, as knowledge improves our naming systems should change. We can track these changes in papers and catalogs, unlike common names.
How to Keep Up to Date with Revisions
The best source for this will always be Catalog of Fishes by William Eschmeyer. Often within days of a scientific paper revising a species this website will update, not just that but it includes all the references and previous names behind all changes.
This is one of the most controversial topics and why not? It involves some really detailed physiology and multiple processes. Generally this means getting your head around things you cannot usually see. I shall only discuss juvenile and adult fishes rather then their eggs here.
First is to understand the anatomy we are discussing in relation to the topic, this is largely the gills found in all fishes.
Figure 1: A diagram of the gills by Campbell, N. A., Reece, J. B., Taylor, M. R., Simon, E. J., & Dickey, J. (2006). Biology: concepts & connections (pp. 70-78). San Francisco, CA: Benjamin Cummings.
The gills while largely known for taking up O2 and release CO2 so have a role in respiration this organ has other purposes. Two major functions are maintenance in osmoregulation and processing of nitrogenous waste, ammonium (NH4+). You can see that the gills are split into gill arches which support two gill filaments, these filaments are then made of many small structures called lamellae (Fig 1). The aim of these structures is to increase surface area so exposure to the water for these purposes.
Another organ that might be discussed is the kidneys, but forget whatever you previously thought about kidneys, fishes kidneys look very different. The structure isn’t really of much use to us but it is generally a thin stretched structure at the top of the fish if curious this website is great for necropsy images: https://www.necropsymanual.net/en/teleosts-anatomy/excretory-and-osmo-regulatory-system/
So lets get into the real physiology.
pH
pH to put simply is a measure of hydrogen ions (H+, reduces the pH) and hydroxide (OH–, increases the pH), it measured in a logarithmic scale so a pH of 6 is 10x more acidic then a pH of 7.
This measure has two main interactions with fishes ammonia excretion and uptake/maintenance of minerals within fishes.
High pH
Ammonia generally exists in two states ammonia (NH3) and ammonium (NH4+). At higher pH levels ammonia is the dominant compound, at lower pH’s it is converted to the safer ammonium. At a higher pH environment the fish has a reduced ability to transport ammonia out of the body, leading to accumulation within the fishes body (Eddy & Handy, 2012; Wilkie & Wood, 1996).
Low pH
It is well known fishes take up calcium (Ca2+) and sodium (Na+) from their environment, it is important for many biological processes. H+, in higher volumes in low pH water competes with calcium and sodium to be taken up by the fishes. In a similar process to how a high pH results in high ammonia accumulation a low pH increases excretion of ammonium (Malabarba et al., 2020). Although a low pH is not particularly toxic (Eddy & Handy, 2012), it does limit access to these compounds. Many fishes who inhabit these environments have evolved different physiological responses to allow them to inhabit such an environment.
One interaction of a low pH would be that this erodes rocks even slowly that can allow for aluminum to accumulate in it’s more toxic form, Al3+(Eddy & Handy, 2012). This shouldn’t be an issue in a well water changed aquarium, but could be a contributor to “old tank syndrome”.
Regardless this is generally discussed at extremes and not usually the parameters we keep our fishes in.
Hardness, the various measures under that name
Hardness maybe is more complex, the aquarium trade associates it largely with KH or GH but realistically there are so many compounds involved that we are not testing for. These compounds are what is discussed in the scientific literature (Malabarba et al., 2020). I prefer TDS or conductivity, not just are these likely the only measures you’ll find for wild fishes.
Low hardness
At a low hardness ionic balance as discussed in the pH section would become difficult. This results in the increase in cells that maintain this balance known as ionocytes (Malabarba et al., 2020).
High hardness
High hardness can result in stress from calcium in the gills, liver and intestines at extreme levels but fishes do show the ability to adapt (Limbaugh et al., 2012).
Adaptability
Many fishes clearly display adaptations to deal with extremes, this depends on the species to it’s ideal range and what it can deal with (Eddy & Handy, 2012; Malabarba et al., 2020). So unless a species has been studied we really don’t know how much they can adapt to.
Summary
It is really difficult to say how compounds interact with fishes in the aquarium context, we are dealing with such a comparatively narrow range of parameters. Recently people have been even avoiding the extremes on the lower side so it’s become difficult to say to much. This topic unlike many is discussing such a wide diversity of taxa and many inhabit variable regions.
References:
Campbell, N. A., Reece, J. B., Taylor, M. R., Simon, E. J., & Dickey, J. (2006). Biology: concepts & connections (pp. 70-78). San Francisco, CA: Benjamin Cummings.
Eddy, B., & Handy, R. D. (2012). Ecological and environmental physiology of fishes (Vol. 4). Oxford University Press.
Limbaugh, N., Romano, N., Egnew, N., Shrivastava, J., Bishop, W. M., & Sinha, A. K. (2021). Coping strategies in response to different levels of elevated water hardness in channel catfish (Ictalurus punctatus): Insight into ion-regulatory and histopathological modulations. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 260, 111040.
Malabarba, L. R., Malabarba, M. C., Baldisserotto, B., Urbinati, E., & Cyrino, J. (2020). Biology and physiology of freshwater neotropical fish. Academic Press.
Wilkie, M. P., & Wood, C. M. (1996). The adaptations of fish to extremely alkaline environments. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 113(4), 665-673.
Choosing fish foods can be very confusing, there are many products on the market all with various claims. The majority of fish diets are formulated based on the nutrition for food fishes, these diets have an aim to have a high growth rate while minimizing costs, efficiency would be the best term. The aim of the ornamental aquarist is far from that, we want a long lived healthy fish with good coloration. The nutritional composition requirements are differ between the two aims (Vucko et al., 2017). This has resulted in many diets not catering for the aim of the fishkeeper and no where is this more obvious then diets aimed at plecos, Loricariids.
The majority of Loricariids are algivores or detritivores, but there is a diversity of dietary niches (Lujan et al., 2015). Contrastingly many products labelled as pleco or algae wafers/pellets contain little to no algae but higher proportions of fish meal (Vucko et al., 2017). The majority of popular Loricariids are along the lines of algivory or feed on various volumes so this should be a focus for the aquarist. Additionally I have yet to see fish ever recorded in the gut of any Loricariid.
These fishes are the most difficult to cater for giving there isn’t quite the selection of algaes available in any diet. Some of them can be difficult for the fish to take to so hence I find Repashy soilent green good and can then be bulked out with even more algae’s.
Catering for Carnivores.
I am not really discussing carnivores so much in this article as there are many diets that cater for them and in recent years with the focus into invertebrates it is only improving. Still, many diets are very high in fish meals, something Loricariids do not consume and nutritionally these do not compare. Not just can fish meals be different nutritionally, the nutrients can be difficult to access (Žák et al., 2022).
The great thing for carnivores is the diversity of frozen foods we have available within the hobby and even fishmongers. Although keep aware for the enzyme thiaminase (in mussels and some fishes) and limit the frequency these are fed to your fishes.
Other niches and specialization.
Fungi hyphae are found in the diets of Panaque, Panaqolus and the Hypostomus cochliodon group and are likely digested, mushrooms or mycoproteins would be the closest to replicating this (Lujan et al., 2011). Sadly most diets don’t contain these. It would be interesting to feed wood that has many of these but usually by the point they have obvious hyphae they are almost entirely broken down.
While Hypancistrus are largely algivores, there is evidence a few of them feed on seeds, read about Hypancistrus here. The exception being Hypancistrus vandragti who seems a little more carnivorous in comparison (Lujan & Armbruster, 2011).
Will they eat it?
Something few consider is that just because a diet might be amazing with ingredients they might not eat it. So there are a range of ingredients such as some herbs used entirely to encourage fishes to eat a diet. This has been the issue I’ve found with some that have great ingredients Repashy super green for example.
Premade diets and their ingredients
Premade diets unlike if you were to make anything yourself entirely will have a reasonable range of nutrients. They are best more as a basis to work from for a more well rounded diet.
From these tables it is easy to understand the varying suitability of different diets to different species and genera. The colour coding is only to give an idea as many ingredients have multiple purposes e.g. fish meal can be a binding agent as well as for nutrition.
Ingredients are ordered in quantity so the top of the list contributes the most.
The hidden issue with premade diets
There is a hidden issue, as you look across the table how similar are many of these diets? Many fishkeepers will buy a range of different products in the aim of diversity of nutrition and ingredients. If so many of the ingredients and the orders are similar this means that there is little diversity, the exception would be there the major ingredients are very different.
Products sold for plecos
Company
Repashy
Product
Soilent Green
Super Green
Bottom scratcher
Morning wood
Dietary Niche
Algivory
Algivory
Carnivory
Xylovory
Summary
Fishes tend to prefer this diet. Contains mostly algae but has a some animal meals but can be bulked out with more algae’s.
Contains no animal products. Fish seem less keen on it. High in algae’s.
Contains a diversity of invertebrates. Shouldn’t be fed as the only diet for non-carnivores as can lead to bloat e.g. Hypancistrus.
No Loricariids digest wood, cellulose is the main ingredient.
Repashy products, coloured by type of product; algae (Dark green), Plant Matter (blue), cereal (Orange), animal matter (red), vitamins (pink), not highlighted might have other purposes such as binding agents or other nutrition.
Repashy unlike the other brands is a gel diet, this means other products such as algae powders can be added in. This means for any of them you can increase the algal composition or add ingredients such as basil.
Company
Fluval
AquaCare
Product
Bug Bites Pleco Sticks
Bug Bites Pleco Crisps
Spirulina Sinking Wafers
Oak
Dietary Niche
Carnivore
Omnivore/cereals
Omnivore
Omnivore/cereals
Summary
A reasonable amount of insects so more ideal then those with more fish meals for carnivores.
A smaller amount of insect meals and contains a wider range of cereals.
Mostly fish meal with a lot of cereals, little algae.
Loricariids cannot digest wood/cellulose nor is it used for digestion. Mostly wheat, which will have limited nutrition and a high amount of fish meal.
Coloured by type of product; algae (Dark green), Plant Matter (blue), cereal (Orange), animal matter (red), vitamins and minerals (pink), not highlighted might have other purposes such as binding agents or other nutrition.
Company
Hikari
Dr Bassler
Vitalis
Product
Algae Wafers
Green
Regular
Pleco Pellets
Dietary Niche
Omnivore
Omnivore
Omnivore
Omnivore
Summary
Not ideal. Contains a lot of fish meal and cereals. A general diet that targets no species.
Very high in cereals and fish meals. Too few algaes to cater for an algivore.
Pretty much the same as the green diet. A lot of fish meal and cereals.
Not ideal. A very general diet that doesn’t cater for any species. Mostly contains fish.
Cereals, fish and fish derivatives, derivatives of vegetable origin, Chlorella pyrenoidosa (5 %), Moringa oleifera (5 %), molluscs and crustaceans, yeast, minerals Additives: Vitamins: E672 Vitamin A 7,500 IE/kg, E671 Vitamin D3 2,500 IE/kg , E300 Vitamin C 500 mg/kg, E307 Vitamin E 260 mg/kg, Magnesium 400 mg/kg, Iron 300 mg/kg, Omega-3 fatty acids 50 mg/g, Vitamin B3 7.5 mg/kg, Chlorophyll 2 mg/kg, Folic acid 2 mg/kg, Selenium 1 mg/kg, Iodine 0.02 mg/kg
Fish and fish derivatives, cereals, molluscs and crustaceans, derivatives of vegetable origin, yeast, minerals Additives: Vitamins: E672 vitamin A 7500 IU/kg, E671 vitamin D3 2500 IU/kg, E300 vitamin C 500 mg/kg, E307 vitamin E 260 mg/kg
Fish and Fish Derivatives, Derivatives of Vegetable Origin, Algae, Oils and Fats, Minerals, Molluscs and Crustaceans.
Coloured by type of product; algae (Dark green), Plant Matter (blue), cereal (Orange), animal matter (red), vitamins (pink), not highlighted might have other purposes such as binding agents or other nutrition.
Company
Oase
Tetra
New Life Spectrum
Fish Science
Product
Organix Veggievore Tabs
Spirulina Wafers
Algae Max
Algae wafers
Dietary Niche
Carnivore
Herbivore
Algivore
Omnivore
Summary
A lot of fish/shrimp meals. Only a small amount of krill.
Plant focused but lacks a lot of algaes.
Beware some have higher fish meal volumes. Otherwise a great range of algaes.
Would benefit from more algaes, the use of mycoproteins is interesting but still a large amount of cereals and fish meal.
Algae (Spirulina & Kelp 15%), Mycoprotein, Cereals, Herring meal, Vegetable protein extracts, Insect meal, Vegetables (Cucumber, Spinach), Molluscs and crustaceans, Yeast, Salmon oil and Garlic.
Coloured by type of product; algae (Dark green), Plant Matter (blue), cereal (Orange), animal matter (red), vitamins (pink), not highlighted might have other purposes such as binding agents or other nutrition.
References:
Lujan, N. K., & Armbruster, J. W. (2011). Two new genera and species of Ancistrini (Siluriformes: Loricariidae) from the western Guiana Shield. Copeia, 2011(2), 216-225.
Lujan, N. K., German, D. P., & Winemiller, K. O. (2011). Do wood‐grazing fishes partition their niche?: morphological and isotopic evidence for trophic segregation in Neotropical Loricariidae. Functional Ecology, 25(6), 1327-1338.
Lujan, N. K., Winemiller, K. O., & Armbruster, J. W. (2012). Trophic diversity in the evolution and community assembly of loricariid catfishes. BMC Evolutionary Biology, 12, 1-13.
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.
Company
Product
Dietary Niche
Summary
Composition (%):
Protein
Fat
Fibre
Moisture
Ash
Ingredients
Coloured by type of product; algae (Dark green), Plant Matter (blue), cereal (Orange), animal matter (red), vitamins (pink), not highlighted might have other purposes such as binding agents or other nutrition.
There are few fishes that really catch the eye as much as the order of true knifefishes, Gymnotiformes. Sometimes confused with some Asian and African species from the group Notopteridae which is within the family Osteoglossiformes, also within that group is the arowana. Gymnotiformes are restricted to South America with the closest relatives being Siluriforme (catfishes) and the tetras (Characiformes) both groups who have a much wider distribution.
Figure 1: Phylogeny of Loricariidae according to molecular information (Tagliacollo et al., 2016): Tagliacollo, V. A., Bernt, M. J., Craig, J. M., Oliveira, C., & Albert, J. S. (2016). Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular phylogenetics and evolution, 95, 20-33.
Gymnotiforme contains 6 families, 36 genera and 272 species (Fricke et al., 2024). Of these species only one is a frequent import, Apternotus albifrons with the common name black ghost knifefish. Other species do appear in the trade but much less frequently otherwise this article would be more specific.
Morphology
The order is generally identified by an eel (anguilliform) shaped body, a large anal fin that extends across the majority of the fishes abdomen, no dorsal/adipose/pelvic fins and; a caudal fin might be present but reduced (Tagliacollo et al., 2016).
The largest Gymnotiformes are in the genus Electrophorus, electric eels of which comprises 4 species, with evidence of individuals reaching over 120cm TL (de Santana et al., 2019). While the smallest might be Hypopygus minissimus at 6.4cm SL (de Santana & Crampton, 2011).
The largest amount of diversity of this family would be in the head shape, there are many with shorter heads and extremely gape limited, others with elongated jaws, some with wide jaws and quite a few with a long snout like mouth. This likely reflects their diet, while all are carnivores there is a wide range of different prey various genera will specialize in (Albert & Crampton, 2005; Ford et al., 2022).
Gymnotus javari
Colouration is extremely variable although they lack any vivid colours the markings differ based likely on the environment. My personal favorite’s for colouration are the various striped members of the genus Gymnotus.
The complexity of dietary specialization
As mentioned earlier Gymnotiformes display a wide diversity of jaw and mouth shapes, some are likely more generalists and others much more specialized. A large number of genus that occur on the rare occasion tend to be these specialists.
Gymnotiformes are all carnivores and many invertivores/insectivores (Gonçalves-Silva et al., 2022; Giora et al., 2014). Some feed on particularly small food items for their relative body size. Lundberg & Mago-Leccia (1986) displayed many species feeding exclusively on plankton regardless of their body size of 8-14cm SL in some of these species. This planktivorous diet is found in many of these long nosed and gape limited species (Giora et al., 2014; Lundberg & Mago-Leccia, 1986). These species simply cannot feed on larger food items and seems to display preferences additionally on the food item. I can only recommend for these trying many different frozen and live foods in a tank with nothing that can compete but even if feeding they can be a challenge and I do not recommend. Feeding these species takes time and requires space for culturing live food, they are probably best species only.
There are genera that do work within captivity although very few. Apternotus albifrons and A. leptorhynchus the brown and black ghost knifefish, not to be confused with a Notopteridae the brown knifefish, Xenomystus nigri from Africa. These have larger mouths that extend so can even feed on tetra but due to their adult size of 30cm SL (Mucha et al., 2021) but in the aquarium some suggest 50cm. This makes them a bit of an undertaking, so the social X. nigri might be a better choice at about 11-15cm SL (Golubtsov & Darkov, 2008). X. nigri has a more extreme arched back, solid grey/black/brown colouring and the anal fin connects directly to the caudal fin. Gymnotus is the other appropriate genus to the aquarium, it is variable in size from around 15cm for Gymnotus javari to 60cm for Gymnotus carapo (Craig et al., 2019). The mouth of Gymnotus doesn’t open as wide as Apternotus and is generally a more shy fish, so would need much less competition. Gymnotus does provide a problem as while there is such a range in size the species provide issues for the fishkeeper in identifying, often small differences. G. carapo vs G. javari is at least easier, the former has the most vivid colouring with distinct black and white wide stripes maybe with spots but I think is slightly more arched in the back.
Sternarchorhynchus aff. mormyrus at night.
Feeding these two genera then if they can be fed on fry foods is the best for the range of vitamins, minerals and general nutrition. Otherwise Gymnotus can be a little more specialized requiring freeze dried, frozen or live foods but are at least generalists. For Gymnotus a range of frozen and freeze dried foods is a must but on top look around for different live foods appropriate for their mouth size, I feed my G. javari earthworms in terms of live foods to avoid those I cannot culture.
This is not typically a genus for the majority of tanks but they are illusive fishes regardless so take the real pet rock fish enthusiast. Gymnotus and two of the Apternotus would be the best choice for the majority of people.
Black ghost knifefish, Apternotus albifrons from Derek Ramsey (2005).
Habitat and setup
Gymnotiforme’s are illusive fishes, they will spend most of their time hiding whether it be in caves or some species will bury themselves in the sand (Escamilla-Pinilla et al., 2019). Therefore a wide diversity of different hiding spaces are a must for these fishes, while some might suggest glass caves given these fishes have eyes they can detect light and dark and would feel safer in a dark area.
There is quite the diversity in habitats but the majority of specialists are maybe more riparian/marginal species. Many of these smaller specialists species would enjoy a habitat with many botanicals or plants (Crampton, 2016) but this might not be possible due to trapping food although if lucky it could encourage smaller invertebrates like ostracods. While others exploit deep channels of water (Evans et al., 2019) therefore without these botanicals or leaf litter but large wood/and or rocks would be present. These found in areas of high botanicals it would be worth considering that they inhabit areas of very low pH and conductivity (Bichuette & Trajano, 2015). Of the larger more adaptable species inhabit a wider range of habitats, Gymnotus is shown to prefer a rocky habitat although can be found at surprisingly high pH (7.6-7.8) and conductivities of (170-190 uScm-1) according to Richer-de-Forges et al. (2009) .
Sociality
As with many fishes there are social Gymnotiformes and those less so. Many are social although as a curiosity Apternotus females are shown to be social whereas the males are ill-tolerant of other individuals (Henninger et al., 2020; Dunlap & Larkins‐Ford, 2003). Similarly Gymnotus javari are suggested to be social whereas the majority of the genus doesn’t tolerate other individuals (Westby & Box 1970; https://www.youtube.com/watch?v=OMRu_YUBE34). The more specialist species seem to be so much more social and even then many fishes seem to learn to feed from each other.
Identification
Outside of the two groups I recommend most the issue has to be identification and I have given clues how to identify a few. There is a lot more diversity and this makes this group tricky. It is certainly a taxa delving into the scientific literature outside of Apternotus where the black and brown ghost knives are obvious. So this does mean Gymnotus is a little risky with obtaining a species that can grow much larger.
Conclusion
To write a whole article about Gymnotiformes without mentioning their amazing electrical abilities, well that doesn’t entirely concern us as fishkeepers with the exception of Electrophorus, the electric eel of which needs an article of it’s own. These are also likely very intelligent fishes who would benefit from a tank that has a variety of decor and landscapes.
References:
Albert, J. S., & Crampton, W. G. (2005). Diversity and phylogeny of Neotropical electric fishes (Gymnotiformes). In Electroreception (pp. 360-409). New York, NY: Springer New York.
Bichuette, M. E., & Trajano, E. (2015). Population density and habitat of an endangered cave fish Eigenmannia vicentespelaea Triques, 1996 (Ostariophysi: Gymnotiformes) from a karst area in central Brazil. Neotropical Ichthyology, 13, 113-122.
Craig, J. M., Kim, L. Y., Tagliacollo, V. A., & Albert, J. S. (2019). Phylogenetic revision of Gymnotidae (Teleostei: Gymnotiformes), with descriptions of six subgenera. PLoS One, 14(11), e0224599.
Crampton, W. G., De Santana, C. D., Waddell, J. C., & Lovejoy, N. R. (2016). Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10), e0161680.
de Santana, C. D., & Crampton, W. G. (2011). Phylogenetic interrelationships, taxonomy, and reductive evolution in the Neotropical electric fish genus Hypopygus (Teleostei, Ostariophysi, Gymnotiformes). Zoological Journal of the Linnean Society, 163(4), 1096-1156.
de Santana, C. D., Crampton, W. G., Dillman, C. B., Frederico, R. G., Sabaj, M. H., Covain, R., … & Wosiacki, W. B. (2019). Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator. Nature communications, 10(1), 1-10.
Dunlap, K. D., & Larkins‐Ford, J. (2003). Production of aggressive electrocommunication signals to progressively realistic social stimuli in male Apteronotus leptorhynchus. Ethology, 109(3), 243-258.
Escamilla-Pinilla, C., Mojica, J. I., & Molina, J. (2019). Spatial and temporal distribution of Gymnorhamphichthys rondoni (Gymnotiformes: Rhamphichthyidae) in a long-term study of an Amazonian terra firme stream, Leticia-Colombia. Neotropical Ichthyology, 17, e190006.
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.
Ford, K. L., Bernt, M. J., Summers, A. P., & Albert, J. S. (2022). Mosaic evolution of craniofacial morphologies in ghost electric fishes (Gymnotiformes: Apteronotidae). Ichthyology & Herpetology, 110(2), 315-326.
Giora, J., Tarasconi, H. M., & Fialho, C. B. (2014). Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PloS one, 9(9), e106515.
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.
Gonçalves-Silva, M., Luduvice, J. S., Gomes, M. V. T., Rosa, D. C., & Brito, M. F. (2022). Influence of ontogenetic stages and seasonality on the diet of the longtail knifefish Sternopygus macrurus (Gymnotiformes, Sternopygidae) in a large Neotropical river. Studies on Neotropical Fauna and Environment, 57(1), 11-17.
Henninger, J., Krahe, R., Sinz, F., & Benda, J. (2020). Tracking activity patterns of a multispecies community of gymnotiform weakly electric fish in their neotropical habitat without tagging. Journal of Experimental Biology, 223(3), jeb206342.
Lundberg, J. G., & Mago-Leccia, F. (1986). A review of Rhabdolichops (Gymnotiformes, Sternopygidae), a genus of South American freshwater fishes, with descriptions of four new species. Proceedings of the Academy of Natural Sciences of Philadelphia, 53-85.
Mucha, S., Chapman, L. J., & Krahe, R. (2021). The weakly electric fish, Apteronotus albifrons, actively avoids experimentally induced hypoxia. Journal of Comparative Physiology A, 207(3), 369-379.
Richer-de-Forges, M. M., Crampton, W. G., & Albert, J. S. (2009). A new species of Gymnotus (Gymnotiformes, Gymnotidae) from Uruguay: description of a model species in neurophysiological research. Copeia, 2009(3), 538-544.
Tagliacollo, V. A., Bernt, M. J., Craig, J. M., Oliveira, C., & Albert, J. S. (2016). Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular phylogenetics and evolution, 95, 20-33.
Westby, G. M., & Box, H. O. (1970). Prediction of dominance in social groups of the electric fish, Gymnotus carapo. Psychonomic Science, 21(3), 181-183.
The Scientific Fishkeeper 