The only member of the family which lives in freshwater. Crepuscular and nocturnal (Ref. 11941). Found in well oxygenated flowing waters and large lakes. Occurs from estuaries of large lowland rivers as well as from small mountain streams, preferring deep waters in summer (Ref. 59043). Also inhabit deep lakes and large rivers (Ref. 5723, 10294) with slow-moving current. Seek shelter under rocks, in crevices on the river banks, among roots of trees and dense vegetation (Ref. 30578, 10294). Those in rivers tend to congregate in deep holes throughout the year, except at spawning (Ref. 27547). Movements into shallower water during summer nights are related to feeding (Ref. 1998). Smaller individuals feed on insect larvae, crayfish, mollusks and other invertebrates with a changing preference for fishes in larger individuals (Ref. 1998, 10294). Source of oil.