Glossary

toxic

Poisonous.

Used in 95 species profiles

ammonia
The chemical compound NH3, which is toxic to fish. The main source in aquaria is the breakdown of protein by a fish's metabolism.
biocide
A chemical agent that is toxic or lethal to living organisms.
chlorine
Highly irritating, toxic, gaseous element of the halogen group typically used as a disinfectant, bleaching agent and in purification of drinking water. Considered harmful to fishes.
ichthyotoxin
Any toxic substance derived from fishes.
nitrates
Any salt or ester of nitric acid, and the end product of the portion of the nitrogen cycle taking place in most closed aquarium systems (the conversion of nitrates to nitrogen gas in natural systems is carried out by anaerobic microorganisms not normally present in sufficient numbers in aquaria, though this process can be induced by installation of a nitrate reactor). While nitrates are less toxic than ammonia or nitrites, they are still potentially harmful to fishes and other aquatic organisms if allowed to accumulate unchecked, and must therefore be diluted via regular water changes. Aquatic plants also help since they are able to metabolise nitrates to an extent.
nitrites
A salt or ester of nitrous acid. Produced in aquaria via metabolisation of ammonia by nitrifying bacteria of the genus Nitrosomonas, and toxic to fishes if present in sufficient concentrations, but in a mature system is further converted into less-harmful nitrates by other bacteria of the genus Nitrospira.