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Threadfin Rainbowfish

Scientific Name: Iriatherina werneri
Family: Melanotaeniidae, Subfamily Melanotaeniinae

About the Threadfin Rainbowfish

Species Type: Freshwater Fish
Category: Atherinids

Care Level: Easy. Does well in a slightly more narrow range of water parameters and shouldn't be used to cycle an aquarium. Will eat most prepared foods. May have some specific care requirements in terms of particular water parameters, social behaviors, food items etc.

Origin: Confined to two populations, one in Western New Guinea and the other in Northern Australia (Allen, 1980). Occurs in slow-flowing or still streams, lagoons, ditches and swamps, in areas of heavy aquatic vegetation including floating plants.

Compatibility/Temperament: Peaceful, but due to its size, flowing fins and sedate manner, it is not recommended for the average community aquarium. Suitable tankmates include th smaller peaceful characins, rasbora, small catfish, dwarf cichlids (Apistogramma, Dicrossus). Should be kept in a group as the males will frequently display if conspecifics are present.


A very beautiful small fish and well deserving of a species aquarium. Water movement must be minimal [note comments on the habitat under Origin], with plenty of plants; floating plants should be provided to shade the light and settle the fish. A dark substrate of fine gravel or sand will further help to calm the fish and bring out their colours. A group of 10 is stunning to look at in a 15 or 20 gallon tank.

Sexes are easily distinguished with males having more and longer black ray extensions on their dorsal and anal fins compared to the females. Threadfin rainbowfish are egg layers and will deposit their eggs among fine vegetation or clumps of Java moss.

H. Meinken described this species in 1974 as the type species for his newly-erected genus; to date it is the only identified living species in the genus. The genus name is Greek, from iris, -idos [= iridiscent] + atherina [= the Greek name of eperlane]. The species epithet honours Werner who first imported the fish to Europe in 1973.


Allen, Gerald R. (1980), "A Generic Classification of the Rainbowfishes (Family Melanotaeniidae)," Records of the Western Australian Museum, 1980.

Meinken, Hermann & W. Foersch (1975), "Iriatherina werneri, a new atherinid fish from New Guinea," in Tropical Fish Hobbyist, volume 4, number 75.

Threadfin Rainbowfish Diet

Naturally feeds on diatoms and micro-crustaceans. Accepts most prepared foods that are small, and supplemental live or frozen foods like brine shrimp, microworms will benefit. Small foods are required due to their narrow throats.


Males attain 2 inches, females close to 1.5 inches.

Minimum Tank Suggestion

18 inches in length (10 gallon) for a small group of six.

Ideal water parameters for Threadfin Rainbowfish

Soft to medium hard (5-12 dGH), acidic (pH 5.5-7.0), temperature 24-30C/75-86F. Clean, stable water is essential, as this species is highly sensitive to nitrates and changes in pH. Smaller but more frequent water changes may be advisable. Plenty of live plants will also help.

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