Red Rainbowfish

Geographical Origin:

The *G. incisus* is micro-endemic: it lives exclusively in nature in only one place in the world, the picturesque Lake Sentani in Irian Jaya (Indonesian New Guinea). This lake has very alkaline water (pH above 7.5). Due to pollution, uncontrolled fishing, and the introduction of exotic predators into the lake, the species is considered vulnerable in nature. Aquarium specimens derive from historical captive breeding.

Morphology:

Compared to *Melanotaenia*, the genus *Glossolepis* is characterized by scales with more strongly crenulated margins, which catch the light differently. The alpha male of the school will develop a grotesquely arched back profile, almost forming a "hump" behind the head, a sign of perfect health and hierarchical supremacy.

Tank Setup and Water Management:

A male *G. incisus* can reach 15 cm (6 inches) in length and is characterized by explosive, straight-line swimming. A 150 cm (5-foot) aquarium (minimum 300 liters / 80 gallons) is the ethical requirement for their housing. The tank must be heavily filtered and sealed with a heavy lid (their instinct to hunt flying insects leads them to make impressive leaps out of the water). The ideal setup involves smooth rocks and dense patches of plants (*Vallisneria*, *Crinum*) relegated to the edges, leaving a massive central "runway".

Color and Sexual Dimorphism:

This is one of the species most misunderstood by beginners because juveniles in stores (4-5 cm / 2 inches) are an insignificant silvery-grey for both sexes. The iridescent red color emerges only in mature males (over 6 cm / 2.5 inches) and only if females (which remain pale yellow/olive) are present to compete for. An all-male aquarium will leave them faded. To achieve the "blood" coloration, the temperature must be kept moderately cool (22-25°C / 72-77°F) and the water alkaline and hard (add mineral salts or limestone rocks if your tap water is too soft).