scat, in biology, any of four species of fishes constituting the family Scatophagidae (order Perciformes). The few species are placed into two genera, Selenotoca and Scatophagus. They are found in marine waters or estuaries of the Indo-Pacific region from the western coast of India to New Guinea and northern Australia and also along the coast of Africa. Occasionally they may enter various freshwater habitats. Scats are known as scavengers, eating decaying plant and animal remains and fecal matter.
The best-known species, the scat, or argus fish (S. argus), is a popular freshwater aquarium fish when small. Scats commonly reach a length of 30 cm (1 foot). The young are colourful little fish with reddish or greenish bodies dotted with black spots, but the adults gradually lose their bright colours and become dull.