Damselfish refers to members of the family Pomacentridae, except those of the two genera Amphiprion and Premnas. Other species within the family have common names that include the word 'damselfish', but in almost all cases this is qualified with an adjective or other descriptor.
The average size of such damselfish is around 3 inches (8 centimeters). They are all marine, however, a couple of species are regularly found in the lower stretches of rivers in pure freshwater, and usually have bright colours. Some species of damselfish are able to adapt well in an average aquarium, but others such as the white-spotted damselfish cannot. The diet of a damselfish can include small crustaceans, plankton, and algae.
Many species of damselfish live in tropical coral reefs, and many of those are kept as marine aquarium pets. However, many also live in temperate climates, such as the damsels inhabiting the coast of southern California and northern pacific Mexican coast.
A common function for Damselfish is as a biological stabilizer in new aquariums. The fish would live in the aquarium during its initial existence, and be used to allow the aquarium to biologically stabilize with beneficial bacteria. This practice is viewed negatively by many aquarists because of the foul conditions the fish are subjected to and the fact that more humane methods to stabilize an aquarium exist.