When the question of feeder fish arises, the debate usually centers around the ethics of using live fish to feed predatory aquarium fish. While this debate is one that should be discussed, it seems to shift focus away from answering a more important question: Is feeding live fish what is best for our predatory pets?
Proponents will claim that they are a cheap and easy way to provide a nutritious meal for their fish. That cheap price tag can only be achieved by culturing feeder fish intensively in crowded systems. The effects of maintaining fish this way have been extensively studied in Atlantic salmon (Salmo salar) raised in sea pens. Fish raised in these conditions display a higher parasite load and are more prone to outbreaks of disease than their wild counterparts. In fact, these sea pens are so susceptible to parasite infestations, that wild fish who live in proximity to these farms display a parasite load higher than fish living in regions without salmon farms (Morton et al, 2008). The risk of transmitting an infection presents a clear threat to the health of our aquatic pets.
Even without the threat of an infection, there is another flaw in the species of fish being sold as feeder fish that is potentially fatal. Goldfish (Carassius auratus), rosy minnows (Pimephales promelas), and white clouds (Tanichthys albonubes) are all members of the family Cyprinidae. Cyprinid fish are known for being fatty and rich in an enzyme called thiaminase. This enzyme catalyzes the breakdown of thiamine, which is more commonly known as Vitamin B1 (Gordon, 2012). A thiaminase-rich diet can result in thiamine deficiency syndrome (TDS), a medical condition characterized by nervous system deterioration (Dreyfus and Victor, 1961). This can result in a myriad of symptoms, but the ones most easily observed are probably: stunted growth, convulsions, and a sudden loss of appetite. If left untreated TDS will result in the death of your fish (Fisher et al, 1995).
Goldfish are so rich in thiaminase that they are a preferred source for isolating thiaminase for use in laboratory studies (Gordon, 2012). Wild predatory fish often eat fish containing less severe quantities of thiaminase, but most wild fish would never eat something as thiaminase-rich as a goldfish. Minor doses are easier to counter a potential deficiency by eating a varied diet. Prey options for a wild fish can be surprisingly diverse, with prey options, like thiamine-rich fish species, insects, shrimps, molluscs, etc.
Even without the threat of an infection, there is another flaw in the species of fish being sold as feeder fish that is potentially fatal. Goldfish (Carassius auratus), rosy minnows (Pimephales promelas), and white clouds (Tanichthys albonubes) are all members of the family Cyprinidae. Cyprinid fish are known for being fatty and rich in an enzyme called thiaminase. This enzyme catalyzes the breakdown of thiamine, which is more commonly known as Vitamin B1 (Gordon, 2012). A thiaminase-rich diet can result in thiamine deficiency syndrome (TDS), a medical condition characterized by nervous system deterioration (Dreyfus and Victor, 1961). This can result in a myriad of symptoms, but the ones most easily observed are probably: stunted growth, convulsions, and a sudden loss of appetite. If left untreated TDS will result in the death of your fish (Fisher et al, 1995).
Goldfish are so rich in thiaminase that they are a preferred source for isolating thiaminase for use in laboratory studies (Gordon, 2012). Wild predatory fish often eat fish containing less severe quantities of thiaminase, but most wild fish would never eat something as thiaminase-rich as a goldfish. Minor doses are easier to counter a potential deficiency by eating a varied diet. Prey options for a wild fish can be surprisingly diverse, with prey options, like thiamine-rich fish species, insects, shrimps, molluscs, etc.
I have heard people claim “success” by keeping an oscar (Astronotus ocellatus) alive for three or four years on a feeder fish heavy diet, but this sounds less like a success when you learn that oscars are capable of living for at least twelve years (Paiva and Nepomuceno, 1989). A poor diet reduces the lifespan of any animal, making it beneficial to replicate the wild diet of your predatory pets. For example, Water Colors Aquarium Gallery maintains a mixed-species group of bamboo sharks (Chiloscyllium spp.) that are fed a diet of frozen krill, frozen silversides, fresh ocean perch fillets, and frozen squid. These dietary decisions are based on studies of the diet of wild bamboo sharks, which is comprised of crustaceans, fish, and cephalopods (Nur-Farhana et al, 2013).
We all keep fish because we love it, but this means we have to accept the responsibility of taking care of another living creature. Each species of fish has spent millions of years adapting to their environment and we should respect that. Google Scholar, a search engine for scientific literature, makes it easier than ever to find reliable sources on the wild diet of any fish you are keeping. The modern aquarium hobbyist has a plethora of frozen foods, fresh seafood, and commercial pellet-foods readily available to them. The benefits of replicating this diet should be obvious, whether you are a seasoned breeder or a novice fishkeeper. When you factor all of that in, it becomes abundantly clear that it is time for everyone to accept the fact that feeder fish have no place in the diet of our aquarium fish.
Literature Cited
Dreyfus, P. and M. Victor. 1961 Effects of thiamine deficiency on the central nervous system. The American Journal of Clinical Nutrition, Vol. 9(4):414–425Fisher, J., J. M. Spitsbergen, T. Iamonte, E. E. Little, and A. Delonay. 1995. Pathological and behavioral manifestations of the “Cayuga syndrome,” a thiamine deficiency in larval landlocked Atlantic salmon. Journal of Aquatic Animal Health, Vol. 7(4): 269-273.
Gordon, E. 2012. Investigations of the source, distribution, expression and physiological function of thiaminase I (Honors Thesis). Cornell University.
Morton, A., R. Routledge, and M. Krkošek. 2008. Sea louse infestation in wild juvenile salmon and Pacific herring associated with fish farms off the east-central coast of Vancouver Island, British Columbia. North American Journal of Fisheries Management, Vol. 28:523-532.
Nur-Farhana, A., A. Samat, Z. C. Cob, M. A. Ghaffar. 2013. Stomach content and trophic level position of two bamboo shark species Chiloscyllium indicum and C. Hasseltii (hemiscylliidae) from south eastern waters of peninsular Malaysia. Journal of Sustainability Science and Management, Vol. 8(1): 113-120.
Paiva, M. P. and F. H. Nepomuceno. 1989. On the reproduction in captivity of the oscar, Astronotus ocellatus (Cuvier), according to the mating methods (Pisces - Cichlidae). Amazoniana, Vol. 10(4): 361-377
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