Cusk Eel

Ophidiiform fish typically have slender bodies with small heads, and either smooth scales, or none at all. They have long dorsal fins, and an anal fin that is typically united with the caudal fin. The group includes pelagic, benthic, and even parasitic species, although all have a similar body form. Some species are viviparous, giving birth to live young, rather than laying eggs. They range in size from Grammanoides opisthodon which measures just 5 centimetres (2.0 in) in length, to Lamprogrammus shcherbachevi at 2 metres (6.6 ft) in length.

The families Ranicipitidae (tadpole cods) and Euclichthyidae (eucla cods) were formerly classified in this order, but are now preferred in Gadiformes; Ranicipitidae has been absorbed within the family Gadidae.

This order includes a variety of deep-sea species, including the deepest known, Abyssobrotula galatheae, found at 8,370 metres (27,460 ft) in the Puerto Rico Trench. Many other species, however, live in shallow water, especially near coral reefs, while a few inhabit freshwater. Most species live in tropical or subtropical habitats, but some species are known from as far north as the coast of Greenland, and as far south as the Weddell Sea.