Taxonomy & naming
Platystacus cotylephorus Bloch, 1794 is the valid name in the Catalog of Fishes and the type species of Platystacus. It belongs to the Aspredinidae, the banjo catfishes. The Catalog of Fishes entry provides no type locality, so none is recorded here. The epithet refers to the egg-carrying habit (Greek kotyle 'cup' + phoros 'bearing').
Morphology
It is strongly flattened from above, with a broad, rather triangular head, small eyes, a long tapering tail, and a smooth skin that bears tubercles. The barbels are small and the pectoral fins stout. Banjo catfishes are superficially leaf-like, and are cryptically coloured in brown. FishBase gives a maximum of 12.5 in SL.
Habitat
FishBase gives its range as Venezuela to northern Brazil, including the lower portions of coastal rivers, in freshwater and brackish water. Aspredinids sit on soft mud and sand, partly buried, and this species is more tolerant of brackish water than most catfishes.
Feeding
Banjo catfishes feed mainly at night on small invertebrates and organic material taken from the bottom. In captivity they take small frozen foods such as bloodworm and brine shrimp and fine sinking foods, and may need to be fed after dark.
Mating
Aspredinids are known for unusual reproductive habits. In Platystacus, the female's belly skin becomes spongy during the breeding season and the eggs are pressed onto it and carried attached on short stalks.
Breeding
The mode of breeding is egg-carrying by the female: fertilised eggs are held attached to the ventral skin until hatching. Captive breeding of this species is not recorded in the sources available to the atlas.
In the aquarium
It needs a soft, fine sand substrate in which it can bury itself, quiet water and dim light, and calm, small tankmates. FishBase lists 72–77 °F, pH 6.8 to 8.2 and hardness of 12 to 35 dH. Because it also lives in brackish estuaries, some keepers add a little salt. Do not keep it with competitive feeders, as it feeds slowly and can starve.
Conservation
The IUCN Red List assessed it as Least Concern in 2020, meaning it is not considered at risk of extinction at present. It is a coastal species and exposed to estuary alteration.