Rosy Bitterling (Rhodeus ocellatus)

Family: Cyprinidae

A spawning-mussel specialist that turns iridescent rose and violet during the breeding season.

Care parameters

Water temperature
14–26 °C
pH
7–8
GH hardness
8–20 dGH
Adult length
5–6 cm
Minimum tank
40 L
Water layer
Mid-water; short-fin bursts
Difficulty
Moderate
Temperament
Peaceful; a true community fish
Origin
Eastern & central China — Yangtze and Yellow basins

Species overview

The rosy bitterling is China's living jewel — a small, deep-bodied carp that depends on freshwater mussels to breed. In the breeding season males flush iridescent rose and violet. In the aquarium it is peaceful, adaptable and fascinating, provided a few mussels or substitute spawning sites are offered.

Native biotope

Habitat
Slow rivers, ponds and lake margins
Flow
Still to gentle
Dissolved O₂
Tolerates low oxygen well

Aquascape & hardware

Substrate
Fine sand; a mussel bed anchors the biotope
Hardscape
Leaf litter and empty mussel shells
Plants
Fine-leaved plants plus open swimming space

Temperament, diet & tankmates

Schooling
Keep 6+; males display in groups
Diet
Omnivore; algae, flakes and small live foods
Recommended tankmates
  • White cloud minnow — Cool-water cousins
  • Rosy barb — Similar size, similar water
  • Nerite snails — Share the same clean-up niche
Avoid keeping with
  • Cichlids — Too aggressive
  • Large labyrinth fish — Fin damage
  • Crayfish — Will eat them overnight

Breeding & notes

Sexual dimorphism
Breeding males turn rose-violet with longer fins; females stay silver with a deeper belly
Breeding method
Mussel spawner. The female deposits eggs inside a freshwater mussel's gills via a long ovipositor; the male fertilizes them at the siphon — fry emerge after 3–4 weeks.

Frequently asked questions

Can bitterlings breed without a mussel?

Practically no. The female needs a living freshwater mussel to receive her eggs, and the larvae develop inside it. One healthy mussel can serve a whole group.

Which mussel species work?

Common pond mussels of the unionid family, such as Anodonta cygnea or Chinese Sinanodonta species available from native-fish suppliers, are the standard choice. The mussel must be alive and healthy.

Are bitterlings aggressive?

No. Males display and chase briefly, but serious harm is rare. They mix well with other small, peaceful, temperate fish.

How long do the eggs stay inside the mussel?

About three to five weeks depending on temperature. Fry emerge as fully formed miniature fish several millimetres long, far easier to raise than most egg-layer fry.

Can I keep them without plants?

You can, but planted tanks transform them — vegetation gives females refuge from males, and the whole shoal colors up when it feels cover is near.