Threadfin Rainbowfish (Iriatherina werneri)



Threadfin Rainbowfish is a small and streamlined fish that can reach up to 5 cm only. Males are different in fin-shape and color from the female. Even the males who are in good health, different environment and diet have different color patterns. The body color is silver. The top levels are in deep blue and the bottom reflects orange colors.

Grown-up examples of this fish distinguish from the youngs by light vertical stripes running along the backbone. The fan-shaped dorsal fin is combined with black, red, orange, and yellow colors. The fin at the pelvis is black or bright yellow while the tail is added with red tips or plain blue.

Female fish is honey-like yellow added with greenish shade and translucent fins. The color patterns of pet fish are usually less bright and attractive than the fish in natural habitat and so is the case with the fish in different rivers at scattered locations.

The fish is widely available for keeping as a pet in the aquarium but not suitable for beginners as it is quite delicate and needs special care throughout.


Threadfin rainbowfish was first described by Meinken in 1974. Another synonym is the Featherfin Rainbowfish. It is found in Indonesia, the south coast of New Guinea between the Fly River and Merauke all across the border of Papua New Guinea. Some population of the species also lives in the Lake Kala and Bosset. Threadfin Rainbowfish naturally lives in slow-moving waterways, clear and also grassy swamps or lagoons, but all with lush vegetation.

They also exist in the Australian swamps of the Edward River and the Jardine River. The good news is that it is not listed on the red list of ICUN. There are records of its population in Australia in several river basins; Queensland State, the Cape York Peninsula, and North-Western Territory. Also, Arnhem Land and Arafura wetland are known for the threadfin rainbowfish population. The locality difference affects the colors of the fish and fins’ morphology. But the wild fish patterns are not found in the tank inhibiting population that is bred for commercial purposes.

In the natural habitats, the fish gathers along the shoreline under the vegetation. Males that are ready to mate have more vibrant colors, they circle these shorelines to attract the female with their vibrant colors to mate.

Tank Conditions:

Temperature: 22-29°C
pH: 4,5 – 7,5
Hardness: 5 – 19 dGH

A densely planted tank with enough space areas is the best living place for them. To add a natural aura to the tank, driftwood, roots, and floating plants will be best for the aquarium decoration. This minimizes the light reaching the tank. No frequent filtration is needed because it basically comes from the sluggish aquatic environment but the well-filtered water especially low in nitrogen compounds (good nitrification) will do best.

Do not release the fish to a tank that is not yet biologically matured. Because the inappropriate water chemistry will harm the fish. This fish is known for its adaptive nature and can happily live in a community tank without aggression. A planted tank is the best place for them with peaceful tank mates.


Iriatherina werneri is an omnivore fish. In their natural habitat, this fish usually feeds on algae with unicellular plankton, insects, diatoms, and different small plant matter that fall in water due they have tiny throat. To maintain their health, their diet should contain flakes that are finely crushed and little live food like mosquito larvae, copepods, daphnia, micro-worms, and brine shrimp nauplii. These all make a nutritious diet for the fish.

A large amount of food can cause serious damage to the fish and biological environment. It is better to buy a small amount of processed food because a large amount of food soon depletes in its nutrition. The amount that the fish can finish in 5 minutes is sufficient to feed for one time. They can be fed several times a day with that small amount of food.



In the mating season, males start displaying their colorful fins to females by frequently circling the areas where they swim together. The intense colors of the body, especially the dorsal and anal fins straighten up and flicker to entice a mate. Upon finding a positive response from a female the couple gets under the cover of vegetation and spawns there. It is always the female who chooses a calm and quiet place under the cover and stays still to completely enter the medium of mating.

The male is capable to mate with several females in a single day. Threadfin rainbowfish scatters its egg under the vegetation and there is no concept of parental care in this species. But, if they even eat their eggs or fry if they will have a chance. Egg-laying usually takes place in higher temperatures over the suggested range. Female lays a few eggs every time during the day until she is fully done.

While breeding in aquariums, two systems are practical. One is to release one male and up to three females in a small tank. Prepared with an air-powered sponge filter with the addition of a spawning medium like aquatic moss ie. Taxiphylum sp. or spawning mops. The spawning medium requires regular checks for the availability of eggs. If there are eggs on it, then you need to shift the medium to another container where the incubation will take place.

The second method is to keep a group of adults in a large tank that is fully prepared for threadfin rainbowfish. The well-planted environment will help the fry to survive. The aquatic moss – Taxiphylum sp.– close to the water surface makes the most favorable condition for the fry because they spend the early days of their life very close to the surface. The same purpose is valid for floating plants with long trailing roots.

The second method is more reliable as the well-set environment of the tank creates favorable water conditions and provides micro-fauna to the new brood which is a nutritious food for them. The first method imposes an artificial environment for hatching the eggs and upbringing the fry which is not reliable for the delicate little creatures.

Old water (loaded with chemicals and organic waste) can cause the fish to die. Small water changes are recommended and leftover foods are also needed to be removed from the tank where the fry is growing. For feeding live food to the fry, multiple types of cultures are necessary. Before breeding it is best to prepare food sources for the fry. The powdered products of good quality are also good for raising them. Feeding the fry twice a day with a very small amount of food will suffice for raising them.

In the early days, fry grows slowly but will grow faster and healthier with live food in the following days. But the smaller fry must be separated from the larger fry because they prey on the smaller ones.

Image Source:,

0 0 votes
Rate This Page
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments