The species reaches up to about 10 cm (4 in) in length, and matures at about 30–35 mm (1.2–1.4 in).

Mainly plant material, and to a lesser extent worms, crustaceans, and insect larvae.

Was this fish used for anything unusual?

Historically, female European bitterlings were injected with human urine as a pregnancy test because pregnancy hormones caused ovipositor protrusion.

What habitat does it prefer?

Clear, slow-running or still shallow waters with plants over sandy or muddy bottoms.

How long do the young remain in mussels?

Young hatch and remain protected within the mussel for about a month before leaving as actively swimming larvae.

Where to See European bitterling While Diving

Q: Where is the European bitterling found?

It occurs in Europe, from the Rhone River basin in France to the Neva River in Russia, in shallow vegetated waters.

Q: How does it reproduce?

Females lay eggs inside freshwater mussels; males release sperm into the mussel's inhalant current to fertilize the eggs, and juveniles stay protected inside the mussel for about a month.

Q: At what age does it become sexual mature?

Both sexes reach sexual maturity in about one year.

The European bitterling (Rhodeus amarus) is a temperate freshwater ray-finned fish in the family Acheilognathidae. It ranges across Europe from the Rhone River basin in France to the Neva River in Russia. Individuals reach up to about 10 cm (4 in). They are found among plants over sandy and muddy bottoms in shallow, clear, slow-running or still waters. Diet consists mainly of plant material, with worms, crustaceans, and insect larvae taken to a lesser extent. Spawning is distinctive: females deposit eggs inside freshwater mussels; males release sperm into the mussel's inhalant current to fertilize the eggs, and the young remain within the mussel for about a month before emerging as swimming larvae. Both sexes reach sexual maturity in about one year at 30–35 mm (1.2–1.4 in). Historically, the species was used in a human pregnancy test where injected urine caused females' ovipositors to protrude if pregnancy hormones were present.

Found among plants in shallow waters; associated with slow-moving or still waters over sandy or muddy bottoms.

Mainly herbivorous (plants), with worms, crustaceans, and insect larvae taken to a lesser extent.

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