Betta Trading

Red Rainbowfish

The Red Rainbowfish, Glossolepis incisus, is endemic to Lake Sentani and the streams flowing into it. This means that it is native to these waterways and does not naturally occur anywhere else in the world.  

Lake Sentani is in the western section of the Island of New Guinea. New Guinea is politically divided into two sections.  The eastern section is the main part of the Independent State of Papua New Guinea, while the western part is the West Papua province of the Republic of Indonesia.  Before 2007 it was called West Irian Jaya.

 It is a beautiful lake that is becoming popular as a tourist destination.  The Red Rainbowfish lives in areas of the lake and surrounding streams that have dense aquatic vegetation.

Water Conditions

Lake Sentani is only 2.6 degrees of latitude south of the equator, and the lake itself is only about 73 metres (240 feet) above sea level.  The area it is in is hilly, so the streams flowing into it will be somewhat higher, but basically the Red Rainbowfish is equatorial and should not be subjected to cold conditions.  A suitable temperature range in an aquarium is between 21 and 28 degrees C (between 70 and 84 degrees F).  The Ph can be between 6.5 and 8.5 but I avoid the extremes and aim for slightly alkaline.  A water hardness of between 8 and 25 dH is acceptable.

This is not a small fish and should not be kept in a small aquarium.  I suggest a minimum of a metre (3 feet) long tank.

The water needs to be kept in good condition and frequent partial water changes are needed as well as a good filter.


This fish comes from areas with a lot of plants.  You should imitate this in an aquarium with these fish.


The Red Rainbowfish is an omnivore and will eat normal fish foods readily.  They benefit from live or frozen foods, but they will also eat plants including Duckweed although they are not quite as keen on this plant as the River Murray Rainbowfish .

Length and Longevity

The maximum size claimed for the Red Rainbowfish is 15 centimetres (6 inches) long, but most of them never reach anywhere near this.  This fish can live for 8 years.


The Red Rainbowfish is a peaceful schooling fish.  The ideal school size for this fish is at least 10 fish of roughly equal numbers of each sex.  This is another reason why it is more suitable for a larger tank.

Although I would avoid putting it with very small fish like Neon Tetras, it is a suitable companion for most peaceful community fish.

Sexing, Temperature and Colour

Only the males get the bright red colour that gives this fish many of its common names.  The females are Olive brown in colour, with clear fins.  Young fish of both sexes also have the female type colouring.  Generally, fish need to be nearly 5 centimetres (2 inches) long to display their adult colouration.

As the males get older their back gets more arched.

The males not displaying their extreme red colours are a dusky brown. 

There are two situations where the males will display their bright red.  At higher temperatures, the dominant male will have the bright red while the other males will not.   At temperatures near the lowest parts of their range, all the males can become bright red. Below is a male and a female.


There are different ways of breeding this fish.  The one suggested here is the one I prefer because it is a bit closer to natural breeding rather than forcing the fish to produce the maximum yield of eggs.

Select the best-looking pair of fish, and put them into a very well planted tank of at least 120 litres (30 US gallons), but the bigger the breeding tank the better.  The plants should include some fine leaved ones like Java Moss.  There should not be any other fish in the tank.

Feed the adults well, including rich live or frozen foods like Daphnia, Mosquito larvae or Blood Worms .  The frequency of feeding is important, and 3 or 4 meals a day is not too much.  If enough live food is available this is easier.

The temperature of the breeding tank can be about 26 degrees C (79 degrees F).  When they are ready the parents-to-be should lay eggs on the plants.  These eggs take 6-7 days to hatch.  The parents usually do not eat their eggs or babies and the family can be kept together.  The parents will continue laying a few eggs a day for extended periods.  The babies will be feeding on infusoria when they first become free swimming.  In a large, well planted tank there will be quite a lot of this, but you can supplement the naturally occurring infusoria with cultured infusoria and with commercial fry foods.  Live Daphnia will provide food both for the parents and the growing babies.

The water quality of the breeding tank is important, so avoid putting in too much of foods that may pollute the water, and very carefully do frequent partial water changes.

For the breeding and growing tank, I prefer air operated sponge filters.


The IUCN Red List classes this fish as vulnerable.   It lives in only one connected set of waterways in an area which is heavily populated and with a rapidly growing human population.  This in itself is a threat because of the rubbish and other waste that can get dumped in the lake and streams.  This increases, both as the human population increases in number, and usually also as it increases in affluence.  That is, unless proper steps are taken to control our pollution, richer people cause more damage to ecosystems than poor people.  This does not have to be so.

A bigger threat is the plan to use Lake Sentani as a fish farming area.  There is nothing intrinsically wrong with fish farming, but the way it is normally done is to bring in exotic species like Tilapia which can potentially wipe out species not adapted to this predator.

The Lake Eacham Rainbow Fish was wiped out in Lake Eacham by the introduction of predatory fish to improve the fishing for recreational anglers.  This was done by fishermen with the apparent approval of the local government of the area.

There is a very real danger that the Red Rainbow fish will join the increasing list of fish species that have been wiped out in the wild by the degradation of their habitats and the introduction of fish not native to the area, and whose extinction is being unfairly blamed on the collection of these fish for aquariums.

Common Names

Although only the males can get the really brilliant red colour, and even then only under specific conditions, many of the names in several languages include a reference to the colour.  Some of these names are: “Red Rainbow Fish”, “Salmon Red Rainbowfish”, “Salmon-red Rainbow Fish”, ‘Red Irian Rainbowfish’, “Arc-en-ciel Rouge Saumon”, “Roter Guinea Regenbogenfisch”, “Lachsroter Regenbogenfisch”, “Kammschuppen-Regenbogenfisch” and “Purppurasateenkaarikala”. 

There are other names referring to meat so they probably have the same idea of redness behind them.  Some of these names are: “радушница гребенчешуйная”, “ 舌鱗銀漢魚 ”, and “ 鳞银汉鱼 ”.

There are only a few common names not referring in some way to the red colouration. 2 of these names are: “Lake Sentani Rainbowfish” and “Irian Jaya Rainbowfish”.

Scientific Name

In contrast to the large number of common names for this fish there is only one scientific name.  This is “Glossolepis incisus” (Weber, 1907).

Sourcesand Picture Credits

The picture of Lake Sentani is by Kiko Turteliny (Flickr: Sentani Lake) [CC BY 2.0 (], via Wikimedia Commons