Boeseman's Rainbowfish

Boeseman's Rainbowfish (Melanotaenia boesemani) is a freshwater fish in the family Melanotaeniidae, endemic to the Ayamaru Lakes region of West Papua, Indonesia, on the island of New Guinea. It is named after Dutch ichthyologist Marinus Boeseman, who helped describe the species. The fish is renowned for its striking two-tone coloration, particularly vivid in mature males, which develops fully as the fish reaches adulthood. Restricted to a small geographic range, Boeseman's Rainbowfish faces conservation concerns from habitat degradation and introduced species within its limited native lake system, though it remains widely bred and popular in the freshwater aquarium trade worldwide.

Boeseman's Rainbowfish is one of the most visually distinctive rainbowfish species due to its sharply divided two-tone coloration.

• Body: deep, laterally compressed, with a slightly arched back typical of rainbowfish
• Color: bluish-violet to steel-blue on the head and front half, transitioning abruptly to bright orange-yellow on the rear half and tail
• Fins: two dorsal fins, tall pointed anal fin, often edged in darker color
• Size: adults reach about 10-12 cm
• Sexual dimorphism: males show more intense, sharply divided coloration and taller fins than the duller, more uniformly colored females This bold two-color split, rather than gradual iridescence seen in many other rainbowfish, is the clearest identifying trait.

Boeseman's Rainbowfish is native exclusively to the Ayamaru Lakes and associated streams in the Bird's Head Peninsula of West Papua, Indonesia, making it one of the more geographically restricted rainbowfish species. It inhabits shallow, clear to moderately turbid freshwater lakes and connecting streams with abundant aquatic vegetation, in warm tropical conditions. The species favors quiet, weedy margins over open water, using vegetation for shelter and feeding. Its restricted native range makes local habitat conditions, including water quality and vegetation cover in the Ayamaru Lakes system, especially important to its wild survival.

Boeseman's Rainbowfish are active, social fish that form loose schools, particularly as juveniles, moving through open water and vegetated margins in search of food. They are omnivorous, feeding on small invertebrates, algae, and plant material found in the water column and among vegetation. Males display their vivid coloration and extended fins during courtship, often engaging in fin displays to attract females and establish dominance among rivals. Spawning involves scattering adhesive eggs among fine-leaved vegetation over consecutive days, with no parental care of eggs or fry. Their activity peaks during daylight hours, and they are considered a hardy, adaptable species within their native lake habitat.