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Care guide · Freshwater · fish

Red rainbowfish

Glossolepis incisa

Red rainbowfish (Glossolepis incisa)
Photo: Hectonichus, CC BY-SA 3.0; resized and compressed. Photo: Hectonichus · Source · CC BY-SA 3.0Resized and compressed; no cropping or colour changes.

The red rainbowfish (Glossolepis incisa) occurs naturally only in and around Lake Sentani in West Papua. Adult males develop a vivid red body and a high-backed profile, while females are generally less brightly coloured. This is an active shoaling fish that needs both space and companions. Sources differ on aquarium temperature and some water values; a field observation from the lake is not the same as captive-care advice. This guide keeps those data separate and uses a stable, cautious overlap for practical care. The species is listed as Endangered (EN) by the IUCN. Ask for documented captive-bred stock rather than assuming origin from a shop label. A long aquarium with open swimming room and planted margins suits it better than a small, densely packed tank.

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At a glance

Temperature
24–29 °C
pH
7.0–8.0
GH
10–20 °dGH
Aquarium length
At least 120 cm
Minimum aquarium volume
At least 108 L
Adult size
Up to 15 cm
Group size
At least 6 individuals
Temperament
Peaceful

About this species

The currently accepted combination in Eschmeyer’s Catalog of Fishes is Glossolepis incisa Weber, 1907, in the family Melanotaeniidae. Aquarium literature often retains the older spelling G. incisus; here it refers to the same species. The fish is endemic to Lake Sentani in West Papua, Indonesia. Seriously Fish lists a maximum standard length of 15 cm; FishBase gives 12 cm SL in its species record. Standard length ends at the base of the caudal fin and is not total length. Males generally become larger-looking, higher-backed and redder as they mature. Females usually remain greyer, olive or silvery.

Natural habitat

The species is associated with Lake Sentani, about 75 metres above sea level in West Papua. FishBase describes it as endemic to this lake, which is also the type locality. Water measurements reported for the natural habitat are field data, not a complete set of aquarium targets. The lake and its surrounding waters form a restricted range, making the fish vulnerable to local change. The IUCN assessment is Endangered (EN); the assessment dated 2019 appears in the 2025-2 Red List data. Aquarium keeping cannot replace conservation: when buying, prefer documented captive-bred stock and do not treat an unverified origin claim as fact.

Aquarium and layout

Provide a long tank. Seriously Fish gives a minimum base of 120 × 30 cm and about 108 litres for a 120 × 30 × 30 cm aquarium. That is the gross geometric volume of those dimensions, not a guarantee that every layout or larger shoal will fit. FishBase mentions a minimum aquarium length of 100 cm; the longer footprint offers more swimming space for an active group of at least six to eight. Plant the margins with robust species and leave the centre open. Attach plants to wood or stone, use gentle to moderate flow and provide effective filtration. Fit a secure lid because active rainbowfish may jump.

Water conditions

Seriously Fish gives aquarium conditions of 24–29 °C, pH 7.0–8.0 and GH 10–20 °dGH. The LICG rainbowfish sheet lists a cooler 22–25 °C band and hard, alkaline water; its species row is narrower than the specialist profile. FishBase reports about 29–30 °C, pH 7.6–8.2 and dH 9–19 for Lake Sentani as habitat context. These are distinct kinds of evidence and should not be merged into one broad range. The 24–25 °C band is a cautious overlap of the aquarium recommendations, not a proven universal optimum. Keep conditions stable, measure your own water and acclimate gradually. GH and KH are different measurements.

Behaviour and group size

The red rainbowfish is peaceful, but large and constantly active. Keep a shoal of at least six, preferably six to eight if the aquarium allows. A group that is too small may be more skittish; mature males display better in the company of their own species. Tiny, slow or timid fish may be unsettled by this species’ size and movement. This guide does not label any individual companion as a verified guaranteed match. Assess proposed combinations by adult size, behaviour, swimming zone, group needs and tank length; matching pH or temperature alone does not prove compatibility.

Feeding

This is an omnivorous fish. Seriously Fish reports that it accepts a range of dry, frozen and live foods; regular variety that includes suitable animal foods supports a varied menu. Offer portions the fish can take readily and check that less dominant individuals also feed. A complete flake food can be one component, not necessarily the whole diet. Dried daphnia is at most an occasional supplement. Prepare frozen foods according to their instructions and remove leftovers. Appropriate particle size depends on the fish and its feeding response; a product name alone cannot guarantee that every individual can eat it easily.

Breeding

The species scatters adhesive eggs among fine-leaved plants or an artificial spawning mop. Seriously Fish describes eggs attaching by a thread, being laid over several days and hatching after about seven to eight days. A separate aquarium with clean, stable water and a mop or fine plants is used for deliberate breeding. Any warmer temperature and alkaline conditions mentioned for spawning belong to the breeding setup and are not a reason to change the regular tank. Check the spawning material frequently and move eggs or larvae if needed. Newly hatched fry are tiny and need very fine food initially; monitor water quality carefully.

Sources & review

This care guide draws on several specialist sources and was last checked on .

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