Warning! At least some species of Selenotoca and Scatophagus have venom glands in the dorsal fin. It is always best to be careful when handling these fish. Although the venom is weak and not dangerous to most people, be aware that those allergic to stings in general may react badly.
There are a number of closely related species traded as argusfishes or scats, usually referred to two genera, Scatophagus and Selenotoca. All are large, active omnivores with a distinct taste for plant material. The insatiable appetite of these fishes is legendary among aquarists. They quickly learn to take novel food items, including flies shot down by archerfishes (see below). Feeding is therefore not a problem and any decent dried or frozen food can be used as the staple diet of these fishes, although some plant material such as blanched lettuce, cucumber, or algae-based flake foods should be offered regularly. Scats need the same sort of aquaria as archerfish and monos: hard, alkaline and brackish water with a specific gravity around 1.010 when mature, and a temperature of 25 to 30° C (77 to 86° F). These are good community fishes, and like monos they are constantly active. Adults need plenty of space: an aquarium of around 120 cm (4 feet) in length and as wide and deep as possible. They also need to be kept in small schools, although they will aso mix well with monos. Scats are basically very robust but they do seem to be prone to ’pop eye’, an infection of the tissues of the eye which causes it to swell. Although not fatal, it is unattractive and difficult to treat and subsides only slowly. Rough handling, coarse netting when moving the fish, and scratches from the aquarium decor are the most likely causes. Changing the salinity of the tank on a regular basis, as with Monodactylus, is another good way to maintain general health.
The genus Scatophagus includes the most widely available fish, and they are found all over the tropical Indo-Pacific. Scatophagus argus is available in a range of colour varieties which may or may not be true subspecies. The commonest variety reaches over 30 cm in length. As a juvenile it is quite rounded in shape with variable colours but basically a spotted brown to green. One variety, the ruby scat Scatophagus argus atromaculatus or ‘Scatophagus rubifrons’, has flecks of red over the body, especially along the back. Both become bronze to silvery brown when mature, with dark spots and a distinctive, hump-backed appearance. The African scat Scatophagus tetracanthus has stripes running vertically on the body when small, but is otherwise similar as an adult.
The silver scats Selenotoca spp. are perhaps more attractive aquarium fishes. Selenotoca is more limited in distribution than Scatophagus, being found only in the New Guinea and Australia. There are two outwardly similar species, Selenotoca multifasciata and Selenotoca papuensis. They never grow so large, reaching about 20 cm. The juveniles and adults are similar in appearance, being a rich silvery white in colour with bold black stripes and spots. The dorsal fin is flecked with red and gold. These fishes usually command a higher price than Scatophagus but a shoal of these lovely fishes is equal in beauty to any reef fish. They are hardy and no more difficult to keep than common scats.
