Bitterling

Rhodeus sericeus amarus (Bloch)

During mating season, males exhibit a deep red underside – but during the rest of the year, the small silver Bitterlings are quite inconspicuous.

Description
Deep-bodied with relatively "tall" profile. Small terminal mouth. Dorsal surface gleaming silver with greenish lateral line extending from the middle of the body to the tail fin. Seldom over 9 cm long.

Distribution
In stagnant and slow-moving waters in Central and Eastern Europe, the Balkans and Asia Minor.

Endangerment and Conservation Status
Indirectly endangered because freshwater mussels are threatened by extinction!

Behaviour
The Bitterling survives on a diet of mostly plant matter and some small animals. Because their eggs are laid in mussels, they require these bivalves for reproduction. Males select one or more mussels for spawning and defend these from competitors.

Special Characteristics
The Bitterling has a complex and fascinating spawning behaviour: during spawning season the female develops a 4 cm-long ovipositor which she uses to deposit eggs one by one in the breathing opening of a mussel. The male then deposits its sperm over the breathing slit and the mussel sucks it into the gill cavity, thus fertilizing the eggs. The male defends the eggs aggressively. Fry are only expelled from the cavity of the mussel after they have developed.