The Featherfin Rainbow (Iriatherina werneri) also known to tropical fish keeping enthusiasts as the Threadfin Rainbow is found between Merauke and the mouth of the Fly River in Papua New Guinea, and Lakes Kala and Bosset.  In Australia, they are found in the numerous river basins of the Cape York Peninsula, Queensland state and in the Northern Territory to the west including the Arafura wetlands of Arnhem Land.

The Featherfin Rainbow is a small, peaceful, streamlined schooling species that only grow to about 2″ in length. Males and females have different color patterns and fin shapes.  Their colors vary greatly depending on the locale where they are collected from, their diet, health, lighting, substrate color, and even their status in the school.

Featherfin Rainbow (Iriatherina werneri)

Males have a silver body with blue highlights above and orange underneath.  Mature males have long threads that extend from their dorsal and anal fins. Their fan shaped primary dorsal fin can be a combination of red, black, yellow, red, or orange.  Their second dorsal fin, anal, and pelvic fins are usually colored black to dark yellow, and their tails are either blue or clear, edged with red.  Adults also have faint vertical stripes that run along their backbone.

Female Featherfin Rainbows have transparent fins, honey colored

Featherfin Rainbow (Iriatherina werneri) female

bodies that are accented with green, and are less colorful than the males.  Wild specimens that genetically originate from different rivers are significantly different in color and fin structure.  Wild specimens are rare in the aquarium trade.

Featherfin Rainbows are a schooling species that are found in grassy freshwater swamps, slow moving streams, clear water billabongs and freshwater lagoons. They are most commonly collected along the banks of heavily vegetated areas in relatively shallow waters that are associated with lily pads.

Juveniles will often form into large groups with the females, where they congregate around fallen branches and shoreline vegetation.

In an aquarium environment, Featherfin Rainbows should be kept in a densely planted aquarium of at least 30 gallon capacity with a dark sand or fine gravel substrate, some floating plants to diffuse lighting, a few river rocks, and some driftwood roots.  These fish do best in a species only tank with at least 6 or 7 of their own kind.  They are easy to keep but prefer little to no current in their tank and are sensitive to swings in water chemistry.  They should only be introduced into biologically mature aquariums.

The Featherfin Rainbow has been bred in an aquarium environment.  They prefer soft to moderately hard water that is slightly acidic (pH 5.2–7.0), at a temperature of 73–84 °F. The male courts the female by repeatedly displaying his colors while raising and lowering his front dorsal fin in front of the female.  When mating takes place, the eggs are scattered among fine leaved plants or clumps of moss, and hatch after 7 to 12 days.  The fry can easily be raised alongside the adults in a species tank if fine leaved aquatic moss like Taxiphylum is present, however the parents should be removed from the breeding tank before the eggs hatch, if no dense cover is present.

Feed the fry infusoria or other microscopic foods until they are able to eat newly hatched baby brine shrimp or finely powdered omnivore flake food.  Start them out with green water for the first few days and add paramecia.

In their natural habitat, Featherfin Rainbows feed on single celled planktonic algae, diatoms, small insects, and other plant matter.  In an aquarium environment, they do best when fed small live foods such as baby brine shrimp, small bloodworms, smaller mosquito larvae, and crushed omnivore flakes.  Like most rainbowfish, they have tiny mouths and smaller throats which can make them difficult to feed.

Iriatherina werneri are commercially bred and readily available in tropical fish keeping shops
and online at moderate prices when they are 3/4″ to 1 1/4″ in length.

Featherfin Rainbow (Iriatherina werneri)

Minimum Tank Size: 30 gallons
Care Level: Easy
Temperament: Peaceful
Water Conditions: 72-77° F, KH 7-10, pH 5.8-6.5
Max. Size: 2″
Color Form: Blue, Grey
Diet: Omnivore
Compatibility: Peaceful
Origin: Asia, Australia, New Guinea
Family: Melanotaeniidae
Life Span: 3 to 5 years
Aquarist Level: Intermediate