New Guinea Red Rainbowfish (Glossolepis incisa)

New Guinea Red Rainbowfish: a large Lake Sentani shoaling fish

The New Guinea Red Rainbowfish is an active, deep-bodied rainbowfish from Lake Sentani in Indonesian New Guinea. Its currently accepted scientific name is Glossolepis incisa; the older spelling Glossolepis incisus remains common in aquarium books, searches and trade listings.

Mature males can develop the rich red colour associated with this species. Females and juveniles are usually olive, bronze or yellowish, and young males may take time to colour. This is therefore a fish to choose for its adult potential, social behaviour and care requirements rather than for a guaranteed shade on arrival.

What you are buying

Each quantity adds one unsexed fish in the approximate size grade selected above. The size selector shows the grades currently available; a listed size is not a promise that every grade is in stock. Sex and final adult colour cannot be guaranteed at juvenile sizes.

The four gallery images are stylised representative illustrations of red adult males, not photographs of the exact fish dispatched. Natural colour, body shape and fin development vary. The image showing two fish illustrates social behaviour; the product is sold per fish unless the quantity selector says otherwise.

Care at a glance

Aquarium and group planning

Plan around the adult group rather than the juvenile dispatch size. FishBase records a minimum aquarium length of 100 cm for groups of five or more, but these fish are strong swimmers and adult males become deep-bodied. A 120 cm aquarium of roughly 250 litres or more gives a group of six a more useful swimming lane, better turning space and greater water stability.

Keep the centre open and place plants, smooth wood or rock around the back and sides. Avoid sharp projections and narrow gaps in the swimming path. A secure lid is essential because rainbowfish can jump when startled or during fast feeding and display.

Six is a practical minimum. A lone fish, pair or trio cannot express normal shoaling behaviour and may become nervous or focus social pressure on one individual. In a mixed group, more females than males can help distribute courtship, although juveniles may be difficult to sex. Every fish should retain access to food and open water.

Water and maintenance

A captive range of 22–27°C works well when temperature is stable. FishBase records warmer 29–30°C water in the natural habitat, but a field measurement is not an instruction to keep the aquarium permanently at that temperature. Warm water carries less oxygen, so surface movement and reliable circulation become increasingly important toward the upper end of the range.

Aim for mineral-bearing alkaline water around pH 7.6–8.2 and 9–19 dGH. Test the source water before ordering and use a repeatable preparation method if adjustment is required. Avoid sudden changes made only to reach an exact midpoint.

Use mature biological filtration sized for the adult group. Ammonia and nitrite should remain at zero, and nitrate should be controlled through measured feeding, regular testing and partial water changes. Match replacement water for temperature and chemistry. The water chemistry guide explains the measurements used on this listing.

Feeding

Use a quality complete rainbowfish pellet, small granule or flake as the nutritional base. Add suitable frozen or trusted live foods such as daphnia, cyclops, brine shrimp, mysis or small insect larvae for variety. A prepared food containing plant-derived ingredients helps provide a balanced omnivorous diet.

Spread food across a broad area so confident adults do not take everything from slower or smaller fish. Offer an amount the group clears promptly, remove leftovers and adjust future portions from body condition and water-test results. Strong feeding enthusiasm does not mean the fish need unlimited food.

Behaviour and tank mates

A settled group normally uses the middle and upper water, turns together and spreads along the open swimming lane. Mature males may become brighter and display side-on. Brief pursuit can be normal, but persistent exclusion, hiding, clamped fins or weight loss requires attention.

Choose robust, peaceful companions with compatible hard-water requirements and a similar feeding pace. Comparable rainbowfish, suitable larger peaceful barbs and sturdy catfish can work when the aquarium provides enough room for every species’ full social group. Avoid tiny fish, timid slow feeders, long-finned fish likely to be stressed by constant activity, known fin nippers and aggressive cichlids.

Browse the current Rainbowfish collection for comparison, but check adult size, chemistry and group needs for each exact species. Closely related rainbowfish can hybridise, so do not distribute mixed offspring as pure stock.

Colour, sex and conservation context

The vivid red adult male shown in the gallery is not a reliable guide to juvenile colour. Maturity, sex, condition, diet, social confidence and lighting all affect appearance. A pale young fish may be healthy, and not every unsexed juvenile will develop the same red body.

The wild Lake Sentani population is assessed as Endangered. That conservation status does not prove that a shop fish is wild caught, locality certified or part of a conservation breeding programme. This listing makes none of those claims. Keep accurate identity records and never release aquarium fish or eggs into the environment.

Arrival and first days

Prepare a fully cycled aquarium before delivery. Check temperature, pH and hardness, confirm strong oxygenation and dim the lights for introduction. Follow the current instructions supplied with the fish, then watch the group for steady breathing, normal swimming and equal feeding. Quarantine is the safest way to reduce the chance of introducing disease to an established aquarium.

Current delivery days, postcode coverage, packaging and claim terms are maintained on the live-fish delivery page.

Care references

Taxonomy was checked against Eschmeyer’s Catalog of Fishes and GBIF. Size, natural-water data, distribution and social guidance were checked against the FishBase species profile. General rainbowfish husbandry was checked against the OATA rainbowfish care sheet.