The primary drawback of feeding live fish is the possibility of contaminating the aquarium with bacteria and parasites. The inexpensive fish that are most likely to be used as feeders have almost always been reared extensively, which means they have been exposed to various pathogens. Feeder fish can, over time, expose predatory fish to skin and gill lice, parasitic intestinal worms, neonatal tetra illness, and a wide range of opportunistic parasites, germs, and viruses. Especially whitespot and velvet which is easy to spread between feeder fish if kept in an overcrowded tank. Most predatory species that eat live fish can also be weaned onto dead alternatives. Some of the species used as feeder fish (
goldfish and
rosy red minnows) contain high quantities of
thiaminase, an enzyme that destroys
thiamine (vitamin B1) and when fed in large quantities can cause nutritional imbalances. When bred and held in an overcrowded or otherwise sub-optimal environment, they may also carry bacterial infections and parasites, which can be passed along to fish that consume them. According to Jessica from " Thiamine Deficiency & fish ". Many products have been called back from the market because they contain thiamine. If a deficiency is detected, many neurological disorders can start forming Thiamine deficiency has been associated with early life-stage death, neurological issues, crippling morbidities, and significant population losses of predatory fish. Since it was first discovered, chronic thiamine deficiency has been linked to fish species kept in aquariums. ==Species use==