European Bitterling Care Guide
Rhodeus amarus is a small native European cyprinid that spawns inside living freshwater mussels and prefers cool tanks.
Compiled by Aquairi from published sources · Published · Updated
Overview
Rhodeus amarus, the European bitterling, is a small native European cyprinid. FishBase records a maximum size around 11 cm. It is best known for its unusual reproductive strategy, in which eggs are deposited inside living freshwater mussels.
Taxonomy
- Family: Cyprinidae
- Genus: Rhodeus
- Scientific name: Rhodeus amarus
Habitat
According to FishBase, the species occurs across central and eastern Europe and northern Asia Minor, in the basins of the North, southern Baltic, Black, Caspian and Aegean Seas. Wikipedia adds a range from the Rhone in France to the Neva in Russia. It is a benthopelagic fish of temperate waters that favours plant cover over sandy and muddy bottoms in shallow areas.
Tank requirements
- Minimum tank volume: 80 L
- Temperature: 4-22 °C (39-72 °F)
- pH: 7.0-8.0
- GH: 8-18 °dGH
- School size: 6 or more individuals
- Lifespan: 4-6 years
Diet
The species is omnivorous. FishBase reports it feeds mainly on plants and to a lesser degree on worms, crustaceans and insect larvae.
Compatibility
European bitterling is a peaceful shoaling fish best kept in groups of six or more with other cool-water native species. It should not be mixed with tropical fish, and a long-term setup ideally includes living freshwater mussels for natural behaviour.
Breeding
FishBase describes a specialised strategy: the female uses an ovipositor to deposit eggs within the valves of a living mussel, and the male sheds sperm into the mussel's inhalant current to fertilise them. Wikipedia notes the eggs remain protected inside the mussel for about a month before the larvae become active.
Conservation status
IUCN Red List: Least Concern (assessed 2022).
Breeding European Bitterling
Overview
The European Bitterling (Rhodeus amarus) is a small native European cyprinid with one of the most specialised reproductive strategies among freshwater fish: it spawns inside living freshwater mussels. The presence of nearby freshwater mussels is of vital importance for breeding.
Sexing
In breeding condition the female develops a long egg-laying tube (ovipositor), historically so distinctive that females were once used in pregnancy tests, protruding their ovipositors after injection with urine from pregnant women. Both sexes reach sexual maturity in one year, at a length of 30 to 35 mm.
Breeding Setup
Provide clear, slow-running or still water, often with a muddy bottom, and house live Unio mussels as the spawning substrate. A cool, unheated tank suits this temperate species. Lifespan is exceptionally up to five years, but most individuals do not survive the year of their first reproduction.
Spawning Behavior & Trigger
The female deposits her eggs inside the valves of a living mussel using her ovipositor. The male sheds his sperm into the inhalant current of the respiring mussel, and the eggs are thereby fertilised within the mussel's gill chamber.
Egg & Fry Care
The young hatch and remain protected within the mussel for about a month, eventually leaving it as actively swimming larvae. The fry remain in the mussel until protection is no longer required, so no separate fry tank is needed during this in-mussel stage.