Flier Rainbowfish

Nematocentris vexillifer is a distinctive rainbowfish named for the remarkably elongated dorsal and anal fins that males develop — vexillum being Latin for flag — which flutter gracefully during courtship displays in a manner quite unlike the typical short fins of most Melanotaenia relatives. The body is silver-blue with iridescent highlights, and the extended fins carry bold black and orange-red markings that are displayed prominently during rivalry and breeding behaviour.

This species inhabits the Sepik River region and associated lowland waterways of Papua New Guinea. It is a moderately available species through specialist importers and has a dedicated following among rainbowfish enthusiasts who appreciate its unusual finnage. Care requirements are typical for a medium-sized New Guinean rainbowfish — moderately hard, slightly alkaline water in a spacious, well-filtered aquarium.

Nematocentris vexillifer breeds in the standard egg-scattering manner of the family. The elongated fins of males are somewhat vulnerable to fin-nipping, so tankmate selection should be made carefully. A species aquarium or quiet community is ideal.

Water: pH 7.0–8.0, temperature 23–28°C, moderately hard; regular water changes maintain fin condition. Tank: Minimum 150 L; open swimming space; avoid strong currents that may impede males with extended fins. Feeding: Quality flake, micro-pellets; live and frozen invertebrates to maintain fin health and colouration. Breeding: Egg scatterer on fine plants; fin-display behaviour makes spawning observation particularly striking. Compatibility: Peaceful; avoid all fin-nippers; best in a species or quiet community aquarium.