deep dorsal notch        mouth             anal fin spines         other
Scatophagidae        present               non-protractile           IV 
Chaetodontidae      not present          protractile               III to V 
Pomacanthidae       not present         protractile                 III              prominent preopercle spine
Drepanidae              present               protractile                 III                 elongate pectoral fins

Scatophagus argus: The body is quadrangular and strongly compressed. The dorsal head profile is steep; snout rounded. 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.  The small, horizontal mouth is not protractile. The teeth are villiform, in several rows on the jaws. Dorsal fin with XI spines and 16-18 soft rays. Spinous and soft segments of dorsal fin separated by a deep notch. The anal fin has IV spines and 14-15 soft rays. Pectoral fins with 16-17 rays. Pelvic fins with I spine and 5 soft rays.  Males have a concave curvature of the head above the eye, whereas in females the head ascends at a constant slope (Barry and Fast 1992). Adults can reach approximately 30 cm TL, but occasionally larger individuals are observed (see Khan 1979).  From Barry and Fast (1992), Kottelat (2001) and Allen et al. (2003).

Juveniles are greenish-brown with either a few large, rounded blotches (approximately the size of the eye) or 5-6 broad, dark vertical bars. Individuals greater than about 4 cm SL have blackish spots (typically slightly smaller than eye) loosely arranged in vertical rows. In large adults, the spots may be faded, and appear only on the dorsal part of the flanks.

It is unclear whether nominal S. argus is in fact composed of more than one species.  Differences in the marking pattern (i.e., bars versus spots, size of spots) of juveniles has lead to contention over whether the species should be partitioned.  The "red scat" (Scatophagus argus rubifrons) may not be a distinct variety of scat, but merely a developmental stage of the common spotted scat (Barry and Low 1992).

See Kottelat (2001) for identification details.

Females mature at about 7-9 months of age and 150 g, while males mature at a smaller size (Barry and Fast 1992).  In the Philippines, spawning is triggered by monsoon rains that begin in June and July and bring rainfall, cooler temperatures, increased river outflows and lower salinities (Barry and Fast 1992).  Eggs are about 0.7 mm in diameter and are transparent and spherical (Barry and Fast 1992).  The larvae hatch about 20 hours after fertilization at a size of 1.8 mm (Chang and Hsieh 1997).

The scat has venomous spines that can inflict painful wounds that ache for several hours (Barry and Fast 1992).

The species has been introduced in Malta (Mediterranean Sea) where it is thought to be established (Zammit and Schembri 2011).  The Maltese population is thought to have arrived via aquarium releases, although the fish now appears occasionally in the fishery.  Interestingly, the spotted scat had been deemed a low risk for introduction and establishment in Malta, as its habitat requirements were considered a poor match for the area (Zammit and Schembri 2011).  The surprising establishment of this species in Malta indicates it may be more flexible with regard to habitat requirements than originally considered.