European Bitterling

The bitterling is a small fish that lives in the slow-flowing, planted fresh waters of Europe and Türkiye. Its most interesting feature is the way it breeds: using a long ovipositor, the female deposits her eggs between the gills of a living freshwater mussel; the young develop inside the mussel and emerge a few weeks later. Breeding males are very colorful, with a purple-blue shimmering body, a turquoise line running toward the tail and a reddish belly.

It is protected in many European countries; neither the fish nor the mussels should be collected from the wild.

• At least 80 liters and 80 cm in length for a group of 6–8.
• 15–20°C is ideal; no heater is needed. For breeding, a cool period of a few weeks at around 10°C in winter is beneficial.
• Sand substrate (for the mussels), dense planting and oxygenated water.
• Because mussels are filter feeders, keeping them alive in an aquarium for long is difficult; a breeding attempt requires knowledge and preparation.

Omnivorous. It feeds on flakes and granules, spirulina, frozen daphnia, brine shrimp and bloodworms.

Peaceful and social. During the breeding season, males defend the area around their chosen mussel as a short-term territory; these chases are harmless.

Good companions: small, peaceful species that like cool water: white cloud mountain minnows, rosy barbs, gold barbs, snails.

Avoid: tropical species that need warm water, large and aggressive fish.