Product Details

Threadfin Rainbowfish – Iriatherina werneri

The Threadfin Rainbowfish is a delicate, elegant rainbowfish known for the spectacular extended fins of mature males and their graceful courtship displays. Also sold as the Featherfin Rainbowfish, Threadfin Rainbow or Werner’s Rainbowfish, this peaceful species is best suited to mature planted aquariums with gentle flow, small calm tank mates and plenty of fine foods. It is a beautiful shoaling fish, but it is easily outcompeted and should not be placed in rough or boisterous community tanks.

Key Identification:

Common Name: Threadfin Rainbowfish
Other Names: Featherfin Rainbowfish, Threadfin Rainbow, Werner’s Rainbowfish
Scientific Name: Iriatherina werneri
Fish Type: Rainbowfish
Water Type: Freshwater

Natural Range & Habitat:

Iriatherina werneri is native to central-southern New Guinea and northern Australia. In the wild, it occurs in slow-flowing streams, swampy ponds, billabongs, drainage ditches and lily lagoon margins where aquatic vegetation is dense and current is gentle.

These habitats provide plant cover, fine food particles, micro-crustaceans and sheltered areas among stems and floating vegetation. In the aquarium, Threadfin Rainbowfish should be kept in a mature planted setup with open swimming space, fine-leaved plants, floating cover and calm water movement.

Appearance & Adult Size:

Threadfin Rainbowfish have a slim, delicate body with a small mouth and elegant fin structure. Mature males are especially impressive, developing long filament-like extensions on the dorsal, anal and pelvic fins, which they use during display. Body colour can show silver, olive, gold, blue, yellow or reddish tones depending on sex, mood, locality and lighting.

Females are usually smaller, plainer and shorter-finned, while males show the best finnage and display colour. Adults usually reach around 3–4 cm, with the fin extensions making mature males appear larger and more dramatic.

Aquarium Suitability:

This species is best suited to peaceful planted aquariums, nano-to-medium displays and specialist small rainbowfish communities. It does well in aquariums with gentle filtration, low stress, fine plant cover and tank mates that will not nip fins or dominate feeding.

Threadfin Rainbowfish are not suitable for aggressive communities, fast-feeding barbs, fin-nipping species or aquariums with strong turbulent flow. Their small mouths and delicate fins mean they need carefully chosen tank mates and appropriately sized foods.

Recommended Aquarium Size:

A practical minimum is 60 litres for a group, with a tank length of at least 60 cm recommended. Larger aquariums are better for bigger groups and more stable water quality.

Keep in a group of at least 6, with 8–10 or more preferred where space allows. A mixed group with several males and females encourages natural display behaviour, while a larger group improves confidence and reduces stress.

Water Conditions:

Temperature: 23–28°C
pH: 6.0–7.5
Hardness: Soft to moderately hard
Additional Notes: Threadfin Rainbowfish prefer clean, stable water with gentle flow and good oxygenation. Avoid strong current, poor water quality, sudden parameter swings and immature aquariums. They show best in planted tanks with floating cover and calm surface movement.

Temperament & Tank Mates:

Aquarium Category: Community Fish

Threadfin Rainbowfish are very peaceful, but they are delicate and can be easily outcompeted. Suitable tank mates include small rasboras, tiny peaceful tetras, pygmy cory-type catfish, Otocinclus, peaceful shrimp in planted aquariums, small ricefish and other calm nano fish that feed gently.

Avoid fin-nippers, boisterous barbs, aggressive cichlids, large predators, fast-feeding rainbowfish and any fish likely to chase or damage the males’ long fins. They should not be kept singly or in pairs, as low numbers make them shy and reduce display behaviour.

Feeding:

Threadfin Rainbowfish are small-mouthed omnivorous micropredators. In nature, they feed mainly on tiny foods such as diatoms, micro-crustaceans and other small organisms. In the aquarium, offer very fine flakes, micro pellets, powdered foods and small floating or slow-sinking foods as the staple diet.

Supplement with suitably sized frozen or live foods such as cyclops, daphnia, baby brineshrimp, rotifers and microworms. Standard large flakes, pellets or chunky frozen foods may be too big. Feed small amounts that are eaten quickly, and make sure they are not outcompeted by faster tank mates.

Behaviour in the Aquarium:

This is a gentle upper to midwater shoaling fish that spends much of its time hovering among plants and open swimming areas. Mature males display by spreading their extended fins and fluttering beside females or rival males.

In a calm planted aquarium, their display behaviour can be one of the main attractions of the species. Breeding may occur in mature setups, with eggs placed among fine-leaved plants, moss or spawning mops. Adults may eat eggs and fry, so separate rearing is needed if you want to raise young.

Care Notes:

Threadfin Rainbowfish need a mature, stable aquarium with gentle filtration and peaceful tank mates. They are sensitive to poor water quality, rough handling and heavy competition at feeding time.

Protect the long fins of males from fin-nippers and avoid strong current. Provide fine foods daily and use floating plants or tall background planting to create security. This species is best introduced only after the aquarium is fully settled and stable.

Recommended For:

Intermediate

Availability:

Occasional / Usually captive-bred or commercially farmed, with wild imports sometimes available

Image Disclaimer:

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Natural variation in size, colour, pattern, fin length, fin shape, body tone and markings can occur between individual fish.