Threadfin rainbowfish

Aquarium fish: Threadfin rainbowfish (Iriatherina werneri)
Size: 4 – 5 cm
Origin: New Guinea
Water temperature: 22-30 ° C
Aquarium volume: 54 l

Threadfin rainbowfish (Iriatherina werneri) – a small, beautifully colored aquarium fish from the rainbow family.


Australia and New Guinea . Fish are found on the Cape York Peninsula in northern Australia and in New Guinea. They live in clean, slowly flowing waters, flooded forests, peat bogs and backwaters. They are often found among dense vegetation less than 1.5 m deep.

Characteristics and disposition

The species reaches up to 5 cm in length. Body laterally flattened. Color silver, variable depending on the place of occurrence. Gender fairly easy to distinguish. Males are slightly larger, more intensely colored and have significantly elongated rays of the dorsal and anal fins.

In nature, it has been observed that females and their young swim in a shoal, and adult males occupy temporary territories where they compete with each other and present their charms to females. In the aquarium, it is recommended to keep in a group of at least 6 individuals , preferably 10 or more. In a large group, they are not only less skittish, but also look more effective and natural. Males also show interesting behavior and the most beautiful colors.

Nutrition and feeding

In the wild, they feed on pythoplankton, diatoms and zooplankton.

In the aquarium, they eat small live, frozen (Daphnia, Artemia, micro nematodes, copepods) and dry food.


They require an aquarium of at least 60x30x30 cm, partially planted, to give these mobile fish enough space to swim. Adding floating plants and roots will dampen the light reaching the tank a bit and give it a more natural look. Filigree rainbows do not like too strong a current of water. They are very sensitive to jumps in water parameters , therefore they should not be introduced to freshly set up aquariums.

They are mild fish and will not be suitable for a general aquarium where they will be easily dominated in competition for food and their long fins will be nibbled. It is best to keep them alone or in a biotope aquarium with fish of the genus Pseudomugil ( Furcatus , Modrook Gertrudy ). For a social aquarium , Otosek , Kirysek Pigmejek , Danio , Razbora and Caridina and Neocaridina shrimps are good choices.


The reproduction of filigree rainbows is difficult . The species spreads its eggs among plants, does not look after its offspring and, moreover, will eat its own eggs and fry whenever there is an opportunity.

In the wild, spawning takes place at the beginning of the rainy season (October to December). During this period, the water contains the most vegetation and food. Spawning takes place during the day, in the late morning hours or early noon, when the water temperature is between 26-28 ° C. In the aquarium, by increasing the temperature, we encourage the fish to breed. A male may have several partners on the same day.

Females lay small amounts of eggs every day for several days. The roe grains are scattered among small-leaved plants to which they attach with sticky fibers. Spawning is preceded by the male courtship. Its coloration becomes more intense. It stretches proudly the front dorsal fin, flapping its dorsal and anal fins intensely at the same time.

Encouraged by this “dance”, the female chooses the place to lay her eggs. Usually they are the roots of floating plants or clumps of small-leaved vegetation. The female freezes in the selected place and then the fish move on to the act of scattering the eggs and releasing the milk. We can breed Werner’s rainbow in a small aquarium, in which we place one male and two or three females. You will need a small sponge filter and a large clump of small-leaved plants or an artificial aquarium mop.

Every day we check if there are any eggs and transfer each noticed to a separate container. An easier and less reliable way is to breed these fish in a large colony of adult specimens, a fully mature and properly equipped aquarium with a lot of plants. In such conditions, the fry are not exposed to changes in water parameters and have constant access to food, and thus have a better chance of survival. The larvae are characterized by high mortality, therefore small amounts of water in the incubation tank should be changed frequently . The fry grow quite slowly in the first weeks, but this process can be slightly accelerated by feeding live micro-foods.

It is best to feed them in small portions several times a day.


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