TankBud

Rosy bitterling

Rhodeus ocellatus

FreshwaterFish

Rosy bitterling (Rhodeus ocellatus)
book74 · CC BY-SA 3.0

Care at a glance

Temperature
64–75°F
18–24°C
pH
6.5–7.5
Adult size
3.1 in
8 cm
Minimum tank
21 gal
80 L
Temperament
Peaceful
Social behavior
Social
Tankmates
With caution
Swim level
Middle
Diet
Omnivore
Difficulty
Easy
Breeding
Egg layer · Hard
Rarity
Common
Family
Acheilognathidae
Origin
East Asia (Amur River basin south to Pearl River basin, Taiwan); introduced elsewhere

Overview

The rosy bitterling is a peaceful coolwater fish for an unheated, planted tank. It is easy to keep.

Did you know

The rosy bitterling and its mussel depend on each other. The mussel shelters the young fish until they swim out, and in return the mussel's own larvae often hitch a ride on the fish.

Caring for the rosy bitterling

Keep rosy bitterlings in a group of six or more, in a tank of at least 21 gal (80 L). They are peaceful and a little shy, and they only settle and color up properly in numbers. Give them dense planting, some rockwork or bogwood to duck behind, and a bit of current. They swim in the middle of the tank.

Keep them unheated at room temperature, 64 to 75°F (18 to 24°C), not in a warm tropical tank running 26°C or higher. Let them have a cooler rest over the colder months. Water on the soft to moderately hard side suits them, with a pH of 6.5 to 7.5.

Rosy bitterlings are omnivores, so feed flake, pellets and frozen or fresh foods. Pair them with other cool-water species such as White Cloud Mountain minnows or other bitterlings, rather than warm tropicals. Never release them into local waterways, and check your local rules before keeping them.

Males color up reddish to purple through the spring and summer spawning season. The fish cannot breed without a live freshwater mussel in the tank. The female grows a long ovipositor and lays her eggs inside the mussel's gill chamber, and the fry emerge after two to four weeks. Breeding is rated hard because keeping a mussel alive long term is the challenge, not the fish.

Good to know

The rosy bitterling, Rhodeus ocellatus, is a member of the family Acheilognathidae and a relative of the carps and minnows. It has established itself outside its native range in some regions.

In the wild

Rosy bitterlings come from rivers and slow, weedy waters across East Asia. They range from the Amur River basin south to the Pearl River basin and Taiwan. These are temperate waters that cool right down in winter.

Symbiotic relationships

Bitterlings and freshwater mussels

Bitterlings do not lay their eggs in the open at all. In spring the female grows a long egg tube and slips her eggs through the outflow siphon of a living freshwater mussel, into its gill chamber, while the male releases sperm over the inflow siphon so the mussel draws it in. The embryos develop inside the mussel for about a month, protected from everything, then swim out. The mussel's own larvae attach to passing fish to develop, so the two use each other. Biologists now read it as a mild parasitism running both ways rather than a partnership: the eggs cost the mussel oxygen and food, and bitterlings have evolved to shed the mussel larvae that other fish carry.

Bitterlings are cool-water fish for an unheated tank and breed only with a live mussel present. Swan or duck mussels are the usual hosts; they are filter feeders that starve in clean water and need a mature, well fed tank with fine sand to sit in, which is why breeding bitterlings is a project rather than a happy accident. Watch the female's egg tube lengthen and the male stake out the mussel, and you have seen the whole ritual.

Every symbiotic relationship in the catalog

Common questions

What size tank does a rosy bitterling need?

A rosy bitterling needs at least 21 gal (80 L). It spends most of its time in the middle.

What temperature and pH does a rosy bitterling need?

A rosy bitterling is comfortable at 64–75°F (18–24°C) with a pH of 6.5–7.5.

What does a rosy bitterling eat?

Rosy bitterlings are omnivores. They eat flake, pellets and frozen or fresh foods.

How big does a rosy bitterling get?

An adult rosy bitterling reaches about 3.1 in (8 cm).

How can you tell a male rosy bitterling from a female?

Males color up reddish to purple through the spring and summer spawning season. Females grow a long ovipositor for laying their eggs.

How does a rosy bitterling breed?

A female rosy bitterling lays her eggs inside the gill chamber of a living freshwater mussel, and the fry emerge after two to four weeks. Breeding is hard because the mussel must be kept alive long term.

Related species