The body is strongly compressed. The dorsal head profile is steep, with a rounded snout. The body is greenish-brown to silvery with many brown to red-brown spots. Spines and rays of the dorsal fin are separated by a deep notch. Small ctenoid scales cover the body. Juveniles are a greenish-brown with either a few large, dark, rounded blotches, or five or six dark, vertical bars.
Since S. argus can live in embayment regions, as well as quite far upstream in freshwater rivers, they can adapt to varying salinities. As fry, they live in freshwater environments, but as they mature, they move to saltwater environments. They do not live in temperate waters, as they require at least a little warmth (21 to 28 °C).
The common scat is omnivorous and an indiscriminate eater. In 1992, biologists Barry and Fast reported adult scat from the Philippines were primarily herbivorous, while the juveniles preferred zooplankton. Although scat were named for their purported habit of feeding on offal (Scatophagus argus is translated from Greek to “spotted feces-eater”), it may be a misnomer as this behaviour has not been confirmed in diet studies.