Fish
European Bitterling
Rhodeus amarus · also called bitterling
In the shallows of a slow river in spring, a female bitterling hovers over a freshwater mussel, her long egg tube extended towards its siphon.
Overview
The European bitterling, Rhodeus amarus, is a Least Concern carp relative of ponds, ditches, and slow rivers across central and eastern Europe. Its strange breeding partnership with freshwater mussels makes it one of the most remarkable small fish in Europe.
A nursery inside a mussel
By laying her eggs in the gills of a living mussel, the female bitterling gives her young a protected, well-oxygenated nursery that few predators can reach.
Status
Least Concern, though it depends on healthy mussel populations.
European Bitterling: common questions
Why does the bitterling need mussels?
The female lays her eggs inside the gills of a freshwater mussel, which shelters the eggs and young fish while they develop.
How does the bitterling lay eggs in a mussel?
The female grows a long egg-laying tube, which she uses to place her eggs inside the gills of the mussel.
How big is a European bitterling?
It is a small fish, usually only 5 to 8 cm long.
Where is the European bitterling found?
It lives in ponds, ditches, and slow rivers with freshwater mussels across much of central and eastern Europe.