Glossolepis incisus

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Glossolepis incisus, also called Red Irian Rainbow, is an iconic rainbowfish from Indonesian New Guinea. Its tall body and vivid colors make it highly valued by aquarists. Mature males usually develop an intense copper-red coloration, especially when displaying or establishing their social rank. Native to Lake Sentani near Jayapura, it prefers warm, well-oxygenated and stable water. Peaceful, active and shoaling, it should be kept in a group in a spacious aquarium. This is a common aquarium species, but successful long-term care still requires enough swimming space, stable water quality and a varied diet.

General species description

Glossolepis incisus is a rainbowfish belonging to the family Melanotaeniidae. It is a shoaling species that usually occupies the middle and upper levels of the aquarium. Individuals are active during daylight and show a visible social hierarchy, especially among males. Keeping several females with a smaller number of males helps distribute displaying and chasing behavior. Mature males can become spectacularly red, while females are often more silvery or brownish. This species is generally peaceful with similarly sized tank mates. It appreciates clean water, good circulation and vegetation that provides cover. Its size and energetic swimming style make it more suitable for a properly sized community aquarium than a small tank. Glossolepis incisus is very common in the aquarium trade, which generally makes it easy to obtain.

Geographic origin and biotope

Glossolepis incisus comes from Indonesia, in the western part of New Guinea, now known as Indonesian Papua. Its natural range is associated with Lake Sentani and surrounding areas near Jayapura. This tropical lake is bordered by hills and receives freshwater from small streams and surface runoff. The fish uses calm shorelines, shallow bays and areas where aquatic or riparian vegetation slows the water movement. The bottom is generally made up of sand, mud and plant debris, with some gravelly or rocky areas. In the aquarium, warm, clear and well-filtered water best reflects its general natural conditions. A temperature of 24 to 28 °C, moderate current and open swimming areas suit this fish well.

Precise locality and local name

The reference locality for Glossolepis incisus is around Lake Sentani, in the Jayapura region of Indonesian Papua. The Indonesian vernacular name most commonly associated with this fish is ikan pelangi merah, meaning “red rainbowfish.” The commercial name Red Irian Rainbow refers to the former name Irian Jaya, which was used for the Indonesian part of New Guinea. In the wild, it uses sheltered shorelines and areas where light passes through dense vegetation. The local population is particularly recognizable by the red coloration of mature males, although intensity varies with age, sex, diet, social rank and water quality. To encourage good coloration, maintain a stable group and avoid overly aggressive or hyperactive tank mates.

Appearance and physical characteristics

Glossolepis incisus has a tall, laterally compressed body, a relatively arched back and a small head. Mature males often show a copper-red to orange-red body crossed by a darker or iridescent lateral band. The fins may display reddish, orange or translucent tones. Females are generally smaller and show more subdued colors, often silver, olive or brownish gold. Its sturdy body shape and energetic swimming are typical characteristics of the genus. The contrast between the back, lateral band and flanks gives males a very distinctive appearance. The commonly cited maximum size is about 15 cm, with females usually remaining smaller. Coloration becomes stronger with a good diet, suitable lighting, the presence of companions and stable water parameters.

General diet

In nature, Glossolepis incisus feeds on small aquatic and terrestrial prey, including insects, tiny crustaceans, larvae and some plant matter. In aquariums, it readily accepts quality dry foods, but its diet should remain varied. Floating or midwater pellets can be supplemented with frozen foods such as brine shrimp, daphnia and mosquito larvae. Small live foods also encourage natural hunting behavior. Offer moderate portions once or twice daily to prevent waste and excessive weight gain. Juveniles benefit from smaller and more frequent meals. A diet containing natural color-enhancing ingredients can support red tones, but it cannot replace genetics, maturity or proper husbandry. A varied diet combined with clean water is essential for maintaining the males’ coloration and the group’s overall vitality.

Essential data

• Native river name: Lake Sentani and surrounding waters
• Local name used: Ikan pelangi merah
• Origin of the scientific name: Name assigned when the species was formally described
• Etymology of the full name: Glossolepis approximately means “tongue-shaped scale”; incisus means “notched” or “incised”
• Common/vernacular names: Red Irian Rainbow, red rainbowfish, ikan pelangi merah
• Family: Melanotaeniidae
• Subfamily: Melanotaeniinae
• Name pronunciation: gloss oh LEP iss in SIGH sus
• Discovery: Max Carl Wilhelm Weber, 1907
• Maximum adult size: Approximately 15 cm
• Water temperature and pH: 24 to 28 °C; pH approximately 7.0 to 8.2
• Watercourse appearance and surrounding vegetation: Calm shorelines, lake bays, warm water, riparian vegetation and sheltered areas
• Typical tank mates: Glossolepis wanamensis, Glossamia gjellerupi, Oxyeleotris fimbriatus
• Temperament and behavior: Peaceful, shoaling and active by day; males display and establish a hierarchy
• Water depth: Shallow to moderately deep shoreline areas
• Sexual dimorphism: Males are larger and much redder; females are smaller and more silvery or brownish
• Bottom structure and flow: Sand, mud, plant debris and gravelly areas; low to moderate flow

In your aquarium

For success with Glossolepis incisus, provide a long, securely covered aquarium with a generous open swimming area and some plants around the edges. Keep it in a group, with more females than males, in warm, clean and well-oxygenated water. Efficient filtration, regular water changes and a varied diet support growth and coloration. Avoid very slow, tiny or aggressive fish. Although this species is commonly available, it still deserves an aquarium suited to its activity level and adult size. Under good conditions, males develop remarkable red coloration and perform fascinating displays that are rewarding to observe.