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Red-tail bitterling

Acheilognathus tonkinensis

Also known as Chinese red tail bitterling, Tonkin bitterling

FreshwaterFish

Care at a glance

Temperature
61–79°F
16–26°C
pH
6.5–7.8
Adult size
4.7 in
12 cm
Minimum tank
40 gal
150 L
Temperament
Mostly peaceful
Social behavior
Schooling
Swim level
Middle
Diet
Omnivore
Difficulty
Medium
Breeding
Egg layer · Hard
Rarity
Rare
Family
Acheilognathidae
Origin
Northern Vietnam and southern China

Overview

The red-tail bitterling is an easygoing, temperate schooling fish for a planted community tank. It is a step up from the easiest fish.

Did you know

The red-tail bitterling also goes by Tonkin rainbow bitterling. The name comes from the way males shimmer in breeding dress.

Caring for the red-tail bitterling

Keep red-tail bitterlings in a group of six or more, in a tank of at least 40 gal (150 L). Kept together, the males color up and display far more than lone fish do. They swim in the middle of the tank, and dense planting, a soft substrate and gentle flow suit them.

The red-tail bitterling needs no heater and does well at 61 to 79°F (16 to 26°C), with a near-neutral pH of 6.5 to 7.8. A cooler season each year helps bring breeding fish into condition.

Feed it as an omnivore, with small frozen foods, flake, sinking pellets and some vegetable matter. It is extremely gentle with tank mates and mixes well with other calm, temperate community fish.

Males take on warm color as they mature. During the breeding season they light up in shifting rainbow colors, while the drab females grow a long ovipositor tube. The female uses it to place her eggs inside a living freshwater mussel, where they develop, which is why aquarium breeding is hard.

Good to know

The red-tail bitterling, Acheilognathus tonkinensis, is a deep-bodied bitterling in the family Acheilognathidae. It is also sold as the Chinese red tail bitterling or the Tonkin bitterling.

In the wild

The red-tail bitterling lives in slow, vegetated streams and backwaters of northern Vietnam and southern China. It stays among plants over soft beds.

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

Weekly picks

Tank mates

The red-tail bitterling is a mostly peaceful, schooling species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.

Check the full mix in the stocking calculator

Common questions

What size tank does a red-tail bitterling need?

A red-tail bitterling needs at least 40 gal (150 L). It spends most of its time in the middle.

What temperature and pH does a red-tail bitterling need?

A red-tail bitterling is comfortable at 61–79°F (16–26°C) with a pH of 6.5–7.8.

What does a red-tail bitterling eat?

A red-tail bitterling is an omnivore. It eats small frozen foods, flake and sinking pellets, plus some vegetable matter.

How big does a red-tail bitterling get?

An adult red-tail bitterling reaches about 4.7 in (12 cm).

Does a red-tail bitterling need a group?

Yes. A red-tail bitterling is a schooling species and should be kept in a group, not singly.

How can you tell a male red-tail bitterling from a female?

Males take on warm color as they mature and shimmer in rainbow colors during the breeding season. Females stay drab and grow a long ovipositor tube.

How does a red-tail bitterling breed?

A female red-tail bitterling uses a long ovipositor tube to place her eggs inside a living freshwater mussel, where they develop. Breeding it in an aquarium is hard.

Related species