There are two genera of argus fish or scats, Scatophagus and Selenotoca. Most authors currently only recognize two species in Scatophagus and one in Selenotoca, in Scatophagus the species S. argus and S. tetracanthus and in Selenotoca the species S. multifasciata. However, there are certainly considerably more species, and in Selenotoca there is probably at least one more, namely S. papuensis. However, this species is currently considered by the vast majority of authors to be a synonym of S. multifasciata. However, they can be distinguished relatively easily by the number of vertical bands and the different shape of the caudal fin. In S. multifasciata there are approx. 10 relatively narrow stripes in the dorsal area. S. papuensis has only about 5-6 clearly wider stripes there. The caudal fin ends in S. multifasciata straight cut to slightly concave (i.e. indented), in S. papuensis it is slightly convex (i.e. curved outwards). However, since, as already mentioned, S. papuensis is currently only considered a synonym of S. multifasciata by the majority of scientists, we refer to all Selenotoca as such in the trade, although it is actually almost always S. papuensis.
Selenotoca are colloquially referred to as “silver scats”. They are widespread throughout the Indo-West Pacific region, but the exact species ranges are unknown because the two species are hardly ever differentiated. Just like “common” scats, they are euryhaline and can move freely between fresh and salt water. A salt content of around 5-10g/l is favorable for keeping these animals, which can grow up to 40 cm (usually 15-20 cm) long in the wild, on a permanent basis. They do not necessarily need salt, but they are very sensitive to two water chemical properties: pH values below 8 and increased nitrite levels. The salt prevents a drop in the pH value (which is why it must be salt for coral reef aquariums in which a pH buffer is added and not ordinary table salt) and the table salt component reduces the toxic effect of nitrite.
Scats are omnivorous and will even eat aquatic plants. A varied diet should therefore be provided. All argus fish are social animals that should be kept in a group of conspecifics if possible. Although there are a few incompatible specimens, these are fortunately the exception. Selenotoca are free spawners without brood care. The males grow significantly larger than the females and have a steeper forehead. The eggs develop in the plankton of the sea, which makes rearing them in the aquarium very time-consuming. For this reason, scats are not bred privately, but they are the subject of aquaculture for food purposes.
For our customers: the animals have code 455001 (3-4 cm) on our stock list. Please note that we only supply the wholesale trade.
Text & photos: Frank Schäfer
