Threadfin Rainbowfish (Iriatherina werneri)

Common Name:

Threadfin Rainbowfish.

Scientific Name:

Iriatherina werneri.

Family:

Melanotaeniidae.

Distribution:

Central and southern New Guinea, northern Australia.

Size:

1.5 - 2.0 inches.

Diet:

They need smaller foods than most fishes as they have a throat with a comparatively small diameter. They are omnivorous, so they'll take live foods and standard foods for tropical community fishes.

Water Temperature:

75 to 82 degrees Fahrenheit (24-28 Celsius).

Water Chemistry:

Soft to moderately hard water is appreciated.

pH:

6.5-7.5.

Life Span:

3-5 years.

Description:

These tiny jewels have the most attractive fins of any of the rainbow fishes. The natural finnage of I. werneri can actually rival the artificially selected finnage of the most attractive Betta splendens.

Like all other rainbow fishes, these have two dorsal fins. The first is fan-shaped while the second has the "threads" for which I. werneri has received its name. The anal fin is likewise a "threadfin".

Bodies are thin, silver and have faded vertical stripes. The bodily fins are all black-based with red/tan overlay. Caudal fins are transparent with red tips and are largely bifurcated. (Females have a pink, not red, tip to their caudal fin.)

Behaviour:

Small, active, and peaceful, they do best in groups of six or more (one male to two females ratio, if possible). They are not for the tank with fishes stressed by activity or for the tank, which has highly active denizens. They need well-planted tanks with open middles so that they may swim but have the security of plants.

The display done by the male for rival males and females involves the elaborate fins.

Minimum Recommended Tank Size:

20 gallons for a small shoal.

Natural Conditions:

They live in swamps and the slow-moving thickly vegetated areas of streams and other flowing waters.

Sexing:

It's all about the fins. Males will have larger, gaudier finnage than their female counterparts. They'll also have more intense colours than the females.

Breeding:

Unlike many hardier rainbows, they can't be counted upon to breed themselves. Near-immaculate conditions, a slight cooling and a decent-sized water change may induce spawning behaviours.

Males start the spawning process by displaying to the females and the spawning almost always takes place in the morning (though you can likely affect the time of spawning by changing the times at which the fish room is light).

These fish will likely have eggs attached to plants. They may be induced to use a spawning mop but there is no guarantee that they would choose that over other plants in the tank.

Microencapsulated fry foods are good starter foods, as are microworms. Anything much larger can and may cause serious damage to a fish whose mouth is large but throat is not.

Miscellaneous:

Their long fins are easy targets for fin-nippers; species tanks are the recommended homes for these fish anyway as they don't breed well with the company of other species.

Be warned: their mouths are large but their throats are narrow. Don't feed overly large foods!

There is a yellow-finned variety that was recently discovered in Queensland.

New Guinean specimens are generally darker than their Australian counterparts.

Photo Credit:

Photo supplied courtesy and ^©Off-ice.