Threadfin rainbowfish

Iriatherina werneri, the Threadfin Rainbowfish, is a diminutive and exceptionally peaceful species from slow-moving streams, swamps, and lagoons in southern New Guinea. Males, the larger sex, reach approximately 4 cm and are distinguished by their elongated dorsal, anal, and pelvic fin filaments that trail beautifully as they swim. The species is schooling by nature and should be maintained in groups of at least 6–10 individuals in a tank with a base of 60 × 30 cm or larger. Threadfin Rainbowfish are adaptable across a wide range of water parameters, with temperatures of 22–30 °C, pH of 5.0–8.0, and hardness of 18–215 ppm. They prefer well-vegetated aquaria with floating plants and dimmer lighting that encourages natural behaviour. Their tiny mouths require appropriately sized foods: live or frozen Daphnia, Moina, Artemia nauplii, and microworms are ideal, supplemented by finely crushed dried foods. They are not suitable for a standard community aquarium, as they are easily outcompeted for food and the long fins of males may be nipped by more boisterous tankmates. Ideal companions include Pseudomugil species, pygmy Corydoras, Otocinclus, and small freshwater shrimp. Males display to one another in open water and court females under floating vegetation, making them a fascinating species to observe in a dedicated planted tank or biotope setup. Spawning is an elaborate daily ritual, with females depositing a few eggs each day among fine-leaved plants over several days.