All fish / Melanotaeniidae

Threadfin Rainbowfish

Iriatherina werneri

Also known as threadfin rainbow, feather fin rainbowfish, featherfin rainbow, werner's rainbowfish, threadfin rainbow fish, iriatherina, イリアテリナ・ウェルネリ, pelangi benang, 丝鳍彩虹鱼, 燕子美人

A tiny, slender rainbowfish whose males grow long thread-like extensions on the dorsal, anal and tail fins, often tipped with red or black. Keepers prize the males' fin displays to each other, which look best in a calm, well-planted tank.

Care at a glance

Care level

Moderate

Temperament

Peaceful

Adult size

4 cm

Temperature

24 to 30 °C

pH

5.5 to 7.5

Smallest tank

60 litres

Keep as

Group of 6 or more, ideally with more females than males

Diet

Omnivore: small live and frozen foods such as baby brine shrimp, daphnia and cyclops, plus fine flake

Swims

Top of the tank

Lifespan

2 to 4 years

Water

Freshwater

Wild range

Southern New Guinea (Indonesia and Papua New Guinea) and northern Queensland, Australia

Breeding

Pairs scatter eggs among fine-leaved plants or spawning mops over several days, and parents ignore but may eat the eggs. Breeding is fairly easy, but the very small fry need infusoria or similar first foods.

Good to know

Their slow swimming and long fins make them easy targets for fin-nippers, and their small mouths mean they can go hungry beside fast, greedy feeders. Keep them only with small, gentle tankmates.