Red Rainbowfish

The Red Rainbowfish (Glossolepis incisus) is a freshwater species endemic to Lake Sentani and its immediate tributary system in Papua, Indonesia, part of the rainbowfish family Melanotaeniidae. It is renowned for the dramatic color transformation males undergo as they mature, developing an intense salmon-red to orange-red body that makes them among the most vivid rainbowfishes in the aquarium trade. Because its entire wild population is confined to a single lake system, the species is considered vulnerable to habitat pressures such as pollution, sedimentation, and introduced fish species, and is listed as vulnerable on conservation assessments. It belongs to the order Atheriniformes alongside other rainbowfishes and silversides.

Adult male Red Rainbowfish are unmistakable, with a deep, laterally compressed body glowing salmon-red to orange across most of the fish.

• Body: deep-bodied silhouette, more rounded than many slender rainbowfish species
• Color: mature males are vivid red-orange; females and juveniles remain silvery-olive with only faint reddish tints
• Fins: rounded, often reddish in males, with two dorsal fins typical of the family
• Size: among the larger rainbowfishes at up to 15 cm The pronounced sexual dichromatism and deep body shape distinguish it from most other Glossolepis and Melanotaenia species, which tend to be more slender or less intensely colored.

Red Rainbowfish are restricted entirely to Lake Sentani and its connected tributary streams in the Papua province of Indonesia, New Guinea. The lake is a large, warm tropical freshwater body (around 25-30°C) with areas of both clear open water and vegetated shallows along the shoreline. The species favors these vegetated margins and inflowing stream mouths, where aquatic plants and submerged structure provide shelter and feeding grounds. Because its entire distribution is limited to one lake system, local environmental changes, including water quality decline from surrounding development, directly affect the entire population. It does not naturally occur in flowing river habitats outside the immediate lake catchment.

Red Rainbowfish form loose shoals that move through open and vegetated areas of Lake Sentani, feeding actively during the day on small invertebrates, insect larvae, algae, and plant matter. Mature males intensify their red coloration and perform fin displays while competing for female attention, establishing informal size-based hierarchies rather than sustained aggression. Spawning occurs repeatedly in warm water, with females scattering adhesive eggs among submerged vegetation or root systems; adults provide no further parental care. Eggs hatch within about a week, and fry begin foraging on microscopic organisms shortly after. As one of the more visually dominant fish in the lake, the species contributes to invertebrate population control while serving as prey for larger fish and birds.