Taxonomy & naming
Rhodeus ocellatus was described by Kner in 1866 as Rhodeus ocellatus, with Shanghai, China as type locality. The Catalog of Fishes gives Rhodeus ocellatus (Kner, 1866) as valid in Acheilognathidae. The bitterlings are a family of their own, sometimes still placed within Cyprinidae in older books.
Morphology
A deep-bodied, laterally compressed small fish. FishBase gives a maximum of 3.5 in SL for males or unsexed fish. Breeding males flush with colour and develop tubercles on the snout.
Habitat
FishBase gives the range as eastern Asia and Taiwan, with records from Russia. It lives in shallow ponds and marshes of the plains and adjacent irrigation canals. The species has been introduced elsewhere, and at least one country reports an adverse ecological impact from it. The recorded temperature is 18 to 24 C and dH 10 to 15.
Feeding
The cached FishBase entry has no diet list. Bitterlings are small omnivores feeding on algae, small invertebrates and plant matter.
Mating
Bitterlings pair up around a freshwater mussel. The male guards the mussel and drives off other males, and the female extends her ovipositor to lay into the mussel's siphon.
Breeding
FishBase says the female lays her eggs inside mussels, where the male fertilises them, and the young remain in the bivalve until they can swim. Breeding therefore needs a healthy living mussel, which makes it a demanding project.
In the aquarium
A peaceful fish for a cool, unheated tank. FishBase gives 18 to 24 C and dH 10 to 15; no pH range is recorded. Keep it in a group with plants and a sand bed. The mussel needed to breed the fish is hard to keep alive, and a bitterling tank should not be set up for breeding without one. Because the species is established outside its native range, never release it.
Conservation
FishBase lists the rosy bitterling as Data Deficient on the IUCN Red List, assessed 4 September 2010. The species is also established as an introduced fish in several regions, and that is a conservation concern in those places.