Angler For Ever

Like other animals, fish can suffer from a wide variety of diseases and parasites. To prevent disease they have a variety of non-specific defences and specific defences. Non-specific defences include the skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. Should pathogens breach these defences, fish can develop an inflammatory response that increases the flow of blood to the infected region and delivers the white blood cells that will attempt to destroy the pathogens. Specific defences are specialised responses to particular pathogens recognised by the fish's body, in other words, an immune response.^[37] In recent years, vaccines have become widely used in aquaculture and also with ornamental fish, for example the vaccines for furunculosis in farmed salmon and koi herpes virus in koi.^[38][39]

Some fish will also take advantage of cleaner fish for removal of external parasites. The best known of these are the Bluestreak cleaner wrasses of the genus Labroides found on coral reefs in the Indian Ocean and Pacific Ocean. These small fish maintain so-called "cleaning stations" where other fish, known as hosts, will congregate and perform specific movements to attract the attention of the cleaner fish.^[40] Cleaning behaviours have been observed in a number of other fish groups, including an interesting case between two cichlids of the same genus, Etroplus maculatus, the cleaner fish, and the much larger Etroplus suratensis, the host.