Threadfin Rainbowfish - Iriatherina werneri

Threadfin Rainbowfish (Iriatherina werneri)

The Threadfin Rainbowfish, Iriatherina werneri, is a delicate and elegant nano rainbowfish with a slender body, soft golden-silver colouration and spectacular extended fin rays in mature males. Also known as the Featherfin Rainbowfish or Werner’s Rainbowfish, this peaceful species is especially impressive in planted aquariums where males can display their long thread-like fins to females and rival males. It is not a boisterous community fish, and is best kept in a calm, mature aquarium with gentle tank mates, small foods and stable water conditions.

Common Name:
Threadfin Rainbowfish, Featherfin Rainbowfish, Werner’s Rainbowfish, Threadfin Rainbow.

Scientific Name (Latin):
Iriatherina werneri

Maximum Size:
Usually around 4–5 cm, with males appearing larger when their extended fin rays are fully developed.

Water Type:
Freshwater

Origin / Natural Habitat:
Native to northern Australia and New Guinea. In the wild, Threadfin Rainbowfish inhabit lowland swamps, slow-flowing streams, drainage ditches, swampy ponds, billabongs and heavily vegetated lagoon margins. They are usually found among dense aquatic plants, lilies and calm marginal cover rather than in fast open water.

Water Parameters:
Temperature: 23–28°C
pH Range: 5.5–7.5
Hardness or Salinity: Soft to moderately hard freshwater; stable, clean water is more important than chasing extremes. Avoid sudden changes.

Temperament:
Very peaceful and delicate. Threadfin Rainbowfish should be kept with calm, similarly sized fish that will not nip fins or outcompete them for food. Mature males display beautifully but are not aggressive. They can become stressed in busy communities with fast, pushy feeders.

Diet:
Omnivorous micro-feeder. In nature, Threadfin Rainbowfish feed mainly on diatoms and tiny crustaceans. In the aquarium, offer fine flakes, micro pellets, powdered foods, frozen daphnia, cyclops, baby brineshrimp and other very small foods. Their mouths are small, so food size is important, and they should not be expected to compete with larger, faster fish.

Minimum Tank Size:
A minimum of 60 litres is recommended for a small group, with 90 litres or more preferred for a larger shoal or mixed planted community. A mature planted aquarium with gentle flow, cover and open display space is ideal.

Behaviour & Activity:
A graceful upper-to-midwater shoaling fish that spends much of its time moving through plants and open water. Keep at least 6 individuals, with 8–10 or more preferred for confidence and natural display behaviour. Males flare their long fins, spread the rounded first dorsal fin and display to females or rival males, especially in the morning or under settled conditions. Eggs are scattered among fine-leaved plants or spawning mops.

Aquarium Category:
Community Fish
Suitable with very peaceful species such as small rasboras, tiny tetras, pencilfish, dwarf Corydoras-type catfish, Otocinclus, peaceful shrimp with caution, snails and other calm nano fish. Avoid tiger barbs, fin-nipping tetras, aggressive cichlids, large predators, boisterous danios, fast-feeding barbs and any fish likely to damage the males’ extended fins.

Special Requirements or Care Notes:
Best kept in a mature, heavily planted aquarium with gentle filtration, floating plants, open swimming pockets and stable water quality. Avoid strong current, rough tank mates and unstable new setups. They are sensitive during transport and acclimation, so introduce carefully and avoid large sudden water changes. A secure lid is recommended, as small active rainbowfish can jump. Males show their best finnage and display behaviour when kept with females in a relaxed group.

Suitable for:
Intermediate fishkeepers

Availability:
Occasional in trade / Captive-bred or specialist import where relevant

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.