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Threadfin ‘Iriatherina’ Rainbow fish

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Described from ‘Merauke, Irian Jaya, Indonesia’ which corresponds to modern day Merauke Regency, Papua province, Indonesia, on the island of New Guinea. It’s distributed along a relatively short section of New Guinea’s southern coast, between Merauke and the mouth of the Fly River across the border in Papua New Guinea, and in the latter watershed has been recorded over 500 km inland. Populations are also known from Lakes Bosset and Kala.

In Australia records exist from numerous river basins of the Cape York Peninsula, Queensland state, plus the Northern Territory to the west, including the Arafura wetland in Arnhem Land. The fish exhibit some differences in colour pattern and fin morphology depending on locality, but wild examples are virtually unknown in the aquarium hobby with all those seen on sale produced on a commercial basis.


Shows a preference for slow-moving streams, freshwater swamps, lagoons, and billabongs containing clear water and abundant macrophytes. It’s most commonly-found in heavily-vegetated, marginal habitats less than 1.5 m in depth and is frequently associated with floating lily pads. A temperature range of 22 – 32°C and pH of 5.2 – 7.5 have been recorded in field measurements.

Females and juveniles have been observed to group together in schools while sexually-active males form temporary territories in open water from which they display to other males and ripe females. Spawning takes place during warmer months of the year.

RM 10.00RM 30.00

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SKU: Threadfin Categories: , , ID: 2727

Maximum Standard Length

30 – 40 mm.

Aquarium Size

An aquarium with base dimensions of 60 ∗ 30 cm should be the smallest considered.


Best kept in a densely-planted tank and an excellent choice for the carefully-aquascaped set-up. The addition of some floating plants and driftwood roots or branches to diffuse the light entering the tankalso seems to be appreciated and adds a more natural feel. If you wish to raise fry alongside the adults the addition of a fine-leaved aquatic moss such as a Taxiphylum sp. is advisable (see ‘Reproduction’).

Filtration does not need to be particularly strong as it mostly hails from sluggish waters and may struggle if there is a fast current. Do not add this fish to a biologically immature aquarium as it can be susceptible to swings in water chemistry.

Water Conditions

Temperature: 22 – 30 °C

pH: 5.0 – 8.0

Hardness: 18 – 215 ppm


Feeds on floating or suspended phytoplankton, diatoms, and other zooplankton in nature, and in the aquarium must be offered items of a suitable size for its tiny mouth. Ideally much of the diet should comprise live foods such as DaphniaMoinaArtemia nauplii, micro worm, copepods, etc., although small/crushed floating dried foods are also accepted.

Behaviour and Compatibility

Very peaceful but not suitable for the general community aquarium since it’s easily outcompeted for food and the long fins of mature males may be nipped at by certain common species. It’s best maintained alone or alongside fishes of comparable size and disposition such as Pseudomugil spp., or if geography isn’t an issue MicrodevarioDanionellaEirmotusTrigonostigma, pygmy Corydoras, small loricariids such as Otocinclus spp., and freshwater shrimp of the genera Caridina and Neocaridina are also suitable.

It’s a shoaling species by nature and really should be kept in a group of at least 6 specimens, ideally 10 or more. Maintaining it in such numbers will not only make the fish less nervous but result in a more effective, natural-looking display. Males will also display their best colours and some fascinating behaviour as they compete with one other for female attention.

Sexual Dimorphism

Adult males possess extended unpaired and pelvic fins, are larger and more colourful than females.


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