Lake Wanam Rainbowfish

The Lake Wanam Rainbowfish (Glossolepis wanamensis) is a freshwater species endemic to Lake Wanam, a small crater lake near Lae in Morobe Province, Papua New Guinea. It is a member of the rainbowfish family Melanotaeniidae and, like its close relative the Red Rainbowfish, exhibits a deep-bodied shape with mature males developing vivid orange-red coloration, while females remain comparatively muted in silvery-olive tones. Because its entire natural population is confined to a single small lake, the species is considered vulnerable to environmental disturbance, including water quality changes and introduced predatory or competitor fish, and it is listed as a conservation concern in regional assessments. It belongs to the order Atheriniformes.

Lake Wanam Rainbowfish are deep-bodied fish reaching about 10-12 cm.

• Body: laterally compressed with a somewhat humped back profile, particularly in older males
• Color: mature males display rich orange-red coloration; females and juveniles are silvery-olive with minimal red tint
• Fins: rounded, often reddish in males, with two closely set dorsal fins
• Tail: slightly forked Its deep-bodied shape and orange-red male coloration closely resemble the related Red Rainbowfish, but the two species are geographically distinct, with this species restricted solely to Lake Wanam rather than Lake Sentani.

Lake Wanam Rainbowfish are found only in Lake Wanam, a small volcanic crater lake near Lae in Papua New Guinea's Morobe Province. The lake is a warm tropical freshwater body with limited surface area, supporting areas of open water alongside vegetated shallow margins where the species tends to concentrate. Because the entire wild population depends on this single small lake, the species' habitat is exceptionally limited compared to most other rainbowfishes, making it highly sensitive to any changes in water quality, sedimentation, or the introduction of non-native fish. It favors shoreline vegetation and structure for shelter and feeding rather than open deep water.

Lake Wanam Rainbowfish shoal loosely near vegetated shallows and shoreline structure within their small home lake, feeding during daylight hours on small invertebrates, insect larvae, algae, and plant material. Mature males display intensified orange-red coloration and active fin movements while competing for female attention, forming temporary loose hierarchies rather than sustained aggression. Spawning occurs repeatedly in warm water, with females depositing adhesive eggs among submerged vegetation or root structures; no parental care follows egg laying. Eggs hatch within about a week, and fry begin feeding on microscopic organisms soon after. Given the lake's small size, the species plays a proportionally significant ecological role in local invertebrate regulation and as prey for other lake fish.