Chinese Bitterling

The Chinese or rosy bitterling is a small subtropical cyprinid reaching 9.2 cm standard length, though a common adult is closer to 5.2 cm. It lives in shallow ponds and plain marshes across eastern Asia and Taiwan, extends into Russia, and turns up in the irrigation canals that connect those waters. It has been introduced well beyond that native range, and at least one country reports adverse ecological effects from those introductions. The IUCN currently lists the species as Data Deficient. Males take on the rosy flush that gives the fish its other common name when they come into breeding condition.

This is a cool-water fish rather than a tropical one, and that single fact decides most of its husbandry. FishBase gives 18 to 24 °C, a pH ceiling of 7.0 with no lower bound published, and a hardness of 10 to 15 dGH. A moderately planted tank of around 80 litres suits a small group, and tankmates should be other temperate species rather than the usual tropical community. Feeding is undemanding, since the fish is omnivorous and takes prepared foods readily.

What makes bitterlings worth keeping is how they breed. The female lays her eggs inside a living freshwater mussel, the male fertilises them there, and the young stay inside the bivalve until they are able to swim out. No mussel means no fry, so a breeding project turns into a question of keeping the mussel alive as much as the fish, and that is the part most aquarists underestimate before they start.