European Bitterling

Rhodeus amarus

FreshwaterFish

Care at a glance

Temperature: 55–72°F (13–22°C)
pH: 6.5–8.0
Adult size: 3.9 in (10 cm)
Minimum tank: 34 gal (130 L)
Temperament: Peaceful
Social behavior: Schooling
Swim level: Middle
Difficulty: Medium
Breeding: No record
Rarity: Very rare
Origin: Europe
Family: Cyprinidae

Overview

European bitterlings are peaceful, shoaling coldwater fish that should be kept in a group of six or more, with a mix of males and females if you hope to see natural behavior. They swim in the middle water and get along well with other temperate, gentle species, making them a good choice for an unheated tank or a cool community. They are undemanding feeders that take flake, small pellets, frozen foods, and some vegetable matter. If you want to breed them you will also need a living freshwater mussel, which is central to how they reproduce. A tank around 130 liters or larger suits a group.

In the wild

The European bitterling is native to slow, weedy lowland waters across much of Europe, including ponds, canals, backwaters, and the quiet margins of rivers where freshwater mussels live. It is a temperate fish, comfortable in cool water of about 13–22 C and a neutral to slightly alkaline pH of 6.5–8.0, and it benefits from a seasonal cool period. Furnish its tank with a soft substrate, dense planting, and open swimming space, and keep the water clean and well oxygenated. A sandy area suits the mussels it depends on for spawning.

Good to know

Rhodeus amarus is a small, deep bodied member of the family Cyprinidae that reaches about 10 cm. It is best known for an extraordinary breeding strategy: the female grows a long tube called an ovipositor and uses it to place her eggs inside the gill chamber of a living freshwater mussel, where the male's milt is drawn in to fertilize them. The young develop in safety within the mussel and swim free after a few weeks. This mussel dependence means it is not casually spawned in a bare aquarium.

Did you know

The bitterling and the freshwater mussel share a two way partnership. The fish shelters its eggs inside the mussel, while the mussel's own larvae, called glochidia, hitch a ride on the bitterling's skin and gills to disperse. During courtship the male turns iridescent pink and purple and defends the mussel like a prized territory.