Threadfin rainbowfish - Iriatherina werneri

Scientific name: Iriatherina werneri

Common name: Threadfin rainbowfish

Family: Melanotaeniidae

Usual size in fish tanks: 4 - 5 cm (1.57 - 1.97 inch)

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Recommended pH range: 6 - 7.5

Recommended water hardness: 2 - 12°N (35.71 - 214.29ppm)

0°C 32°F30°C 86°F

Recommended temperature range: 24 - 29 °C (75.2 - 84.2°F)

The way how these fish reproduce: Spawning

Where the species comes from: Oceania

Temperament to its own species: peaceful

Temperament toward other fish species: peaceful

Usual place in the tank: Top levels

General Information

Threadfin Rainbowfish (Iriatherina werneri) is a delicate, peaceful nano rainbowfish from slow, plant-choked creeks and swamps of southern New Guinea and northern Australia. Males display spectacular, filamented fins and courtship dances; a proper group (8–10 ) encourages natural behaviour and reduces shyness. Adults reach about 4–5 cm.

Food & Feeding

Despite a willing appetite, the species has a tiny mouth and narrow throat. Offer ultra-fine foods: powdered quality flakes/micro-granules, freshly hatched brine shrimp nauplii, daphnia (sieved to small size), cyclops, microworms, vinegar eels, and fine frozen fare (rotifers, cyclops). Feed small portions 2–3× daily; avoid coarse pellets.

Sexing

Males are more colourful with markedly elongated, sail-like dorsal/anal fins and filamented rays; females are smaller, plainer, and rounder-bodied.

Breeding

A continuous/spawning-mop breeder. Use a separate, gently filtered tank with fine-leaved plants or mops. Slightly cooler, fresh water changes often trigger courtship. Adults scatter adhesive eggs over days; either remove mops to a hatching box or keep adults light on density/feeding. Eggs typically hatch in ~7–10 days (temperature-dependent). Start fry on infusoria/rotifers, then baby brine shrimp once large enough.

Lifespan

Typically 3–5 years with stable, clean water and an appropriately fine diet.

Tank Requirements & Water Parameters

Tank size: from 60 cm (24″) length for a group; open swimming lane plus dense planting and floating cover.
Temperature: 24–29 °C (75–84 °F) for long-term care; brief higher peaks are tolerable but avoid sustained >30 °C.
pH: 6.0–7.5 (soft to mildly hard). Stability matters more than the exact number.
Hardness: soft to moderate (≈ 2–12 °dH).
Filtration/flow: gentle sponge or diffused outflow; they dislike strong current. High oxygenation without blasting flow.
Aquascape & light: dark substrate, dense plants, floating cover for diffused light; calm surface preferred.
Maintenance: weekly water changes; avoid abrupt parameter swings.

Compatibility & Tank Mates

Peaceful and timid. Ideal companions are small, calm species that won’t outcompete them for micro-foods: small rasboras, tiny tetras, peaceful shrimp/snails, and gentle pygmy Corydoras. Avoid fin-nippers, boisterous fish, and large fast feeders.

Behaviour & Usual Place in the Tank

Active in the upper/top levels, especially under floating plants. Males display to one another; keep a ratio of 1 male to 2–3 females or multiple males with ample line-of-sight breaks.

Short Description

Threadfin Rainbowfish (I. werneri) is a graceful nano rainbow for quiet, planted aquaria: ultra-fine diet, gentle filtration, soft to moderately hard water, and stable warmth yield the best colours and flowing fins.