Emerald Rainbowfish

From Microcosm Aquarium Explorer

Glossolepis wanamensis - Allen & Kailola, 1979
Emerald Rainbowfish

Glossolepis wanamensis.jpg

Also called the Lake Wanam Rainbowfish, a green rarity. Photo © Neil Armstrong.

Overview

Hailing from a single small lake west of Lae in Papua New Guinea, this is a rare and prized rainbowfish that takes on iridescent green hues when mature. It develops a deep body form like its more common genus mate the Red Rainbowfish, and it has a grandly exaggerated anal fin.

Courting males are spectacular fish, and mature rainbowfishes are frequently in a reproductive mood.

Juveniles are rather ordinary looking, as are many immature rainbowfishes, but come into their glorious own if well fed for several months. Sexual maturity among the rainbows generally arrives at the age of six months, and well-kept fish can live to five or more years of age.

Juvenile. Photo by Johnny Jensen.

Since they were described by Dr. Gerry Allen in 1979, the sole body of water where they have been found has become infested with introduced African Mossambique Tilapia (Oreochromis mossambica), threatening the native rainbows. Virtually all rainbowfishes sold to aquarists are captive-bred.

Threatened in Wild?
According to Adrian Tappan in his enormously informative rainbowfish accounts (see below):

"C. Ellway first collected this species in 1975 but it wasn't until 1979 that they were scientifically described. This followed their collection by Gerald R. Allen et al in October 1978. A few live specimens were transported to Australia but failed to become established in the hobby. Barry Crockford brought more live specimens to Australia in 1979. Five survived, which included only one female. A year later further live specimens were collected but again only one female survived. This small captive population formed the basis of all the aquarium stock that was available until 1992.

Fisherman on Lake Wanam. Photo by Heiko Bleher.

"In 1992, Heiko Bleher collected live specimens from the Lake and introduced them to the European hobby. He again collected in 1994 and reported that introduced Tilapia populations had increased dramatically and only managed to collect seven Glossolepis wanamensis males and one female. He returned in 1995 and noted that Tilapia infestation of the Lake had increased even further and only two very old male specimens were collected. He reported in Aqua Geögraphia, Volume 16 that Glossolepis wanamensis was becoming extinct in the Lake.

However, a more recent survey (1999) by a team from ANGFA, Melbourne Zoo and the Rainforest Habitat in Lae, found that Glossolepis wanamensis were in reasonably large numbers in the Lake, but that a coloured variety of the Banded Rainbowfish, Chilatherina fasciata, found in the lake on previous collecting trips had all but disappeared."

Because the rainbowfishes readily interbreed, some so-called Emerald Rainbowfishes sold to aquarists are, in fact, crossbreds of unknown stock. Enthusiasts (who sometimes call themselves "bowheads") keep prices high for known pure strains of Glossolepis wanamensis.

Family: Melanotaeniidae

Other common name(s):

  • Laka Wanam Rainbowfish

Native range:

Habitat: Rainbowfishes will adapt to most aquarium spaces as long as they have room to exercise their athletic swimming abilities. They do best with open water fringed by driftwood, large plants, and/or rocks.

Maximum length: 9 cm (4 in)

Water: Freshwater 26 °C (79 °F) - 30 °C (86 °F)

General swimming level: Midwater to top.

Feeding

Omnivore. Rainbowfishes are greedy eaters and easy to satisfy. Offer a variety of meaty foods, high-quality flakes, and color-enhancing rations. Feedings of enriched, frozen brine shrimp or mysis shrimp will help condition breeders.

Aquarium Compatibility

Rainbowfishes of all species are ideal community members, active but mainly interested in chasing around with their own kind. This is generally harmless, but males may skirmish and they can persistently drive females in a desire to spawn, leading to tattered fins. A good stocking rule for rainbows is one male to two or three females.

Many are too large for the small or beginner's aquarium.

Breeding/Propagation

Spawn adhesive eggs in fine-leaf vegetation or a spawning mop. In good condition, rainbowfishes will shed six to 40 eggs daily. Fry hatch in about 12 days and are easy to raise in well-established aquarium with a natural population of infusoria. The fry of G. wanamensis are reported to be larger than those of other species.

For a good overview of rainbowfish breeding, see: Breeding Rainbowfishes.

Notes

Some of the best online rainbowfish information is available at: Rainbowfishes/National Library of Australia.
Further Reading: The Fishes of Sahul, a fascinating journal about the fishes and aquatic life of Australia and New Guinea: ANGFA.

Text credit: JL