Fish
Threadfin Rainbowfish
Iriatherina werneri
Origin: The threadfin rainbowfish lives in northern Australia and southern New Guinea. It inhabits slow streams, swamps, lagoons, and backwaters with dense soft-leaved vegetation and clean, soft, warm water.
Also known as: Threadfin rainbowfish, Iriatherina werneri
Fact sheet
- Size
- 5 cm
- Lifespan
- 4 years
- Minimum tank size
- 60 L
- Temperature
- 24–30 °C
- pH
- 5.5–7
- Hardness GH
- 2–8 °dH
- Temperament
- Peaceful
- Social behavior
- Schooling
- Group size
- 6+ individuals
- Swimming zone
- Middle, Top
- Diet
- Omnivore
- Jumps out
- No
- Eats plants
- No
Overview
The threadfin rainbowfish is an elegant miniature rainbowfish famous for its incredibly long, thread-like fin rays. Males perform striking displays, spreading their fins and sparring with one another, making the species one of the most beautiful of nano fish. For all its flair it is a peaceful and somewhat timid fish with a tiny mouth that needs calm tankmates and small food. Keep it as a shoal with several males in a densely planted tank with clean, soft water. It is an excellent choice for a calm species or nano aquarium.
Appearance
The body is small and elongated, 4–5 cm long. The base colour is silvery-brown with a bluish sheen. The highlight is the two dorsal fins and the anal fin with greatly elongated thread-like rays, nearly black in males; the tail has drawn-out upper and lower lobes. Males are noticeably showier with larger fins; females are plainer. In display the male raises all its fins.
Care
A tank of at least 60 L, densely planted with soft-leaved plants, with calm water and gentle flow. Temperature 24–30 °C, pH 5.5–7.0, hardness GH 2–8. Stable parameters, soft clean water, and regular water changes are needed. Dark substrate and diffuse light bring out the colour; floating plants are beneficial.
Feeding
An omnivore with a very small mouth. Food must be tiny: micro-pellets, crushed flakes, and small live or frozen fare — brine shrimp nauplii, cyclops, micro-worm, and infusoria. The fish cannot swallow large food. Feed 2–3 times a day in small portions.
Compatibility
A peaceful, timid fish. Ideal for nano tanks with small rasboras, microrasboras, dwarf tetras, corydoras, and shrimp. Active or large tankmates frighten it and outcompete the slow threadfin. Keep in groups of 6–8 with several males for displays.
Breeding
Breeding is possible but needs patience. The fish lay small eggs on soft-leaved plants or spawning mops over several days. Remove the adults and move the eggs to a rearing tank. The tiny fry need infusoria and 'green water' — the hardest stage.
Fun facts
The thread-like fin rays of males can exceed half the body length. The males' tournament displays with spread fins are harmless and serve courtship. The species is named after a German aquarist and fish collector.