Special adaptations

Within the considerable diversity of fish there are less-usual attributes of some species which facilitate survival in particular habitats or in response to selective pressures. The intense competition in warm, shallow water results in polymorphism in colour and size and complex social structure in some reef-fish and in different dentitions in cichlids with trophic specializations. Fish in the light-less deep sea are typically dark with large eyes and mouth; often they possess light-emitting photophores. In contrast, dark-dwelling cavefish lack melanin pigmentation, are usually pink, lack photophores and generally have poor eyesight. Adaptations to other limited habitats such as desert springs or temporary pools and water margins favour small fast-growing fish and air-breathing fish adapted to terrestrial habitats. The range of special adaptations is considerable, including burrowing fish, sound-producing fish, electric fish and even ‘flying’ fish. While parasitic fish are rare, special symbiotic relationships occur, as does hermaphroditism.