Emerald Rainbowfish

The Emerald Rainbowfish (Glossolepis wanamensis) is a freshwater fish in the family Melanotaeniidae, native to Lake Wanam near Lae in Papua New Guinea. Like its close relative the Salmon-red Rainbowfish, it belongs to the genus Glossolepis, characterized by deep, laterally compressed bodies and pronounced sexual dichromatism. The species was scientifically described in 1985 and, due to its restricted single-lake distribution, is considered to have a naturally limited range. It has become a popular aquarium species internationally, valued for the striking iridescent green coloration developed by mature males, which contrasts with the muted tones typical of females and juveniles.

Emerald Rainbowfish reach roughly 8-13 cm, with males noticeably larger and deeper-bodied than females.

• Body: deep, laterally compressed, arched dorsal profile in males
• Male coloration: brilliant iridescent emerald-green overall
• Female/juvenile coloration: duller olive to silvery-green
• Fins: two dorsal fins; translucent yellow-green unpaired fins
• Tail: forked The vivid, uniform emerald-green body of mature males, combined with the deep Glossolepis body shape, distinguishes this species from Melanotaenia rainbowfish, which more typically show striping or spotting rather than solid iridescent coloration.

This species is endemic to Lake Wanam, a small lake near Lae in Morobe Province, Papua New Guinea, and its associated inflow and outflow streams. It occupies warm tropical lowland freshwater, typically near vegetated margins as well as more open lake water. As with other single-lake endemic rainbowfish, its entire wild population depends on the health of one water body, making it inherently vulnerable to localized habitat disturbance such as sedimentation, pollution, or changes in water level. It thrives in stable, well-vegetated lake conditions typical of lowland Papua New Guinea.

Emerald Rainbowfish school in open water and along vegetated lake margins, foraging during the day on small invertebrates, algae, and other organic matter in an opportunistic, omnivorous manner. Males display their brightest emerald coloration during courtship, competing for the attention of females near plant cover or submerged structure; eggs are scattered and adhere to vegetation, receiving no further parental care. As with other Glossolepis species, social structure is loosely hierarchical among males based on size and color intensity. Within Lake Wanam's ecosystem, it functions as both a consumer of small invertebrates and a prey item for larger fish and birds.