Threadfin Rainbowfish

Looks how to spot one

Scaled, slender nano rainbowfish with long fin filaments

A tiny, slim fish famous for the long, thread-like extensions on the males' fins. Males have the biggest fins and strongest colours, so the sexes are easy to tell apart. When displaying, a male raises his first dorsal fin and flicks his trailing fin threads.31

Personality what they are like

Gentle and peaceful, but shy at feeding time and easily outcompeted, so it does best in a species tank or with other small, calm fish.1

Daily activity how busy a day looks

Moderately active shoaling fish that likes to hang near floating plants and display in open areas.1

Grooming and care the hands-on bits

Needs a mature, stable tank and steady water conditions; Seriously Fish does not recommend it for beginners. Choose tankmates that will not nip the males' long fins.1

Home where they are happiest

Minimum tank base about 60 x 30 cm (around 54 litres). Temperature 22-30 °C, pH 5.0-8.0, hardness 1-12 dGH. Dense planting with floating plants and gentle flow.12

Food basics what goes in the bowl

Has a tiny mouth. In nature it eats diatoms, plankton and tiny crustaceans; in the aquarium offer small live foods such as baby brine shrimp, Daphnia, Moina and microworms, plus finely crushed dry food.123

Company who they like around

Keep at least 6, ideally 10 or more; a ratio of about one male to three females suits breeding.13

The story where it all began

Herman Meinken described it in 1974 from fish collected near Merauke, naming it after the German fish importer Arthur Werner. The genus name combines Irian (Jaya) with the silverside genus Atherina, because it was first thought to be related to silversides.32

Recognised by the official bits

IUCN Red List

Least Concern (assessed February 2019)2

Taxonomy

Family Melanotaeniidae; the only species in the genus Iriatherina, described by Meinken in 19741