TankBud

Threadfin rainbowfish

Iriatherina werneri

Also known as Thread fin rainbow

FreshwaterFish

Threadfin rainbowfish (Iriatherina werneri)
NRJMelvinT · CC BY-SA 4.0

Care at a glance

Temperature
72–86°F
22–30°C
pH
6.0–7.5
Adult size
1.6 in
4 cm
Minimum tank
13 gal
50 L
Temperament
Peaceful
Social behavior
Schooling
Swim level
Middle
Difficulty
Medium
Breeding
Egg depositor
Rarity
Rare
Family
Melanotaeniidae
Origin
New Guinea, Australia

Overview

The threadfin rainbowfish is a small, delicate schooling fish for a calm, planted community tank. It is best kept by someone with a little experience.

Did you know

The male threadfin rainbowfish carries some of the longest, most elaborate fins in the whole rainbowfish family. In display he spreads them wide, like small flags.

Caring for the threadfin rainbowfish

Keep threadfin rainbowfish in a group of eight or more, with several males so they display their long, trailing fins to one another. Aim for a tank of 13 gal (50 L) or larger. Plenty of fine-leaved and floating plants over a fine substrate gives the males space to show off. Add some leaf litter as well.

Keep the water calm and clean, with very gentle flow. Hold it at 72 to 86°F (22 to 30°C) and a pH of 6.0 to 7.5. Threadfins have small mouths, so offer fine foods such as crushed flake, micro pellets, frozen cyclops, daphnia and baby brine shrimp.

They are delicate and peaceful, and they swim in the middle of the tank. Choose calm, slow tank mates. Faster fish will outcompete them at feeding time and may nip their flowing fins, and the males' trailing threads are fragile.

Males grow long, thread-like dorsal and tail fins as they mature, which make them look much larger than they are. Threadfins scatter small eggs among fine plants and mops over an extended period and give no parental care. The fry hatch very small and need tiny live foods in their first days.

Good to know

The threadfin rainbowfish is Iriatherina werneri, a member of the rainbowfish family Melanotaeniidae. It is the only species in its genus.

In the wild

Threadfin rainbowfish live in northern Australia and southern New Guinea. They keep to clear, still and slow-moving waters such as swamps, lagoons and vegetated stream edges. These waters are warm, soft and slightly acidic to neutral.

Weekly picks

Tank mates

The threadfin rainbowfish is a 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 threadfin rainbowfish need?

A threadfin rainbowfish needs at least 13 gal (50 L). It spends most of its time in the middle.

What temperature and pH does a threadfin rainbowfish need?

A threadfin rainbowfish is comfortable at 72–86°F (22–30°C) with a pH of 6.0–7.5.

What does a threadfin rainbowfish eat?

A threadfin rainbowfish has a small mouth, so it needs fine foods. Offer crushed flake, micro pellets, frozen cyclops, daphnia and baby brine shrimp.

How big does a threadfin rainbowfish get?

An adult threadfin rainbowfish reaches about 1.6 in (4 cm).

Does a threadfin rainbowfish need a group?

Yes. A threadfin rainbowfish is a schooling species and should be kept in a group, not singly.

How can you tell a male threadfin rainbowfish from a female?

Males are the ones with long, thread-like dorsal and tail fins. These grow in as they mature and make the fish look much larger.

How does a threadfin rainbowfish breed?

Threadfin rainbowfish scatter small eggs among fine plants and mops over an extended period and give the eggs no care. The fry hatch very small and need tiny live foods for their first days.

Related species