Mussels form an essential part of their reproductive system, with bitterling eggs being laid inside them. Long thought to be symbiotic with the mussels (whose larval phase attaches to fish gills during development), recent research has indicated they are, in fact, parasitic, with co-evolution being seen in Chinese bitterling and mussel species.
Bitterlings usually reside in areas with dense plant growth. They are hardy fish and can survive in water that is not very well oxygenated. They grow to be 3–4 in (76–102 mm) long at most. The bitterling's diet consists of plant material and small larvae of insects.
Colour variation
Transparent scale variants of bitterlings occur, though not commonly, and are exploited in the aquarium trade.
Additional field notes
Bitterling reproduction depends on living freshwater mussels.
Sources: Rhodeus sericeus species summary
Development inside a mussel
FishBase describes the female placing eggs within a freshwater mussel using an elongated ovipositor. The young later leave this refuge at about 10 millimetres in length, roughly 28 days after hatching. This stage of the life cycle ties successful reproduction to suitable mussel hosts as well as to the fish’s own habitat.
Sources: Rhodeus sericeus species summary
Article text: Wikipedia contributors, Amur bitterling (source revision). Licensed under CC BY-SA 4.0. Retrieved 2026-10-11.
