The Millennium Rainbowfish is a show piece, nobody can pull the color red quite like this beauty!

The Millennium Rainbowfish Glossolepis pseudoincisus is a gem from the Indonesian islands. This fish has a bold red coloration and the personality to match. It is a hardy and lively fish. If well kept, mature males will reward the aquarist by displaying their fins and coloration (and displaying their big egos too). It’s really no wonder that in a few short years, this amazing species has taken the international fish market by storm.

With pristine water the Millennium Rainbowfish are easily kept in your community tank and adds a ton of color and excitement. These fish are active and outgoing and will definitely liven up the aquarium. They can be kept with similar sized tank mates that are playful and social but not aggressive. They are a schooling fish that do best with about 6 or more of their own kind. Keep a good ratio of males and females and the males will stay busy posturing each other, brightly popping out as they display their most brilliant colors.

This rainbowfish, also known asTami River Rainbowfish and Lake Ifaten Rainbowfish, has a short but interesting history. As the story goes, this fish was first accidentally discovered almost a half a century ago, but somehow it could never be found again in the river. Fifty or so years later, this species was found in a previously uncharted and unknown lake located in Western New Guinea (formerly Irian Jaya), now called Lake Ifaten.

This very remarkable finding came just at the turn of the real millennium (2001), giving this species the common name Millennium Rainbowfish to honor its discovery. The Millennium Rainbowfish looks very similar to the Red RainbowfishGlossolepis insicus, however it has smaller scales and is a smaller fish. But because of the similarities in appearance and geographic location it has been given the scientific name G. pseudoincisus.

For more Information on keeping freshwater fish see:
Guide to a Happy, Healthy Freshwater Aquarium

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Atheriniformes
  • Family: Melanotaeniidae
  • Genus: Glossolepis
  • Species: pseudoincisus
Millennium Rainbowfish – Quick Aquarium Care
  • Aquarist Experience Level: Intermediate
  • Size of fish – inches: 4.0 inches (10.16 cm)
  • Minimum Tank Size: 35 gal (132 L)
  • Temperament: Peaceful
  • Aquarium Hardiness: Moderately hardy
  • Temperature: 70.0 to 79.0° F (21.1 to 26.1&deg C)
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Habitat: Distribution / Background

The Millennium Rainbowfish Glossolepis pseudoincisus was described by Allen and Cross in 1980. It is known from  lakes in West Papua New Guinea (formerly Irian Jaya) in Indonesia. Other common names it is known by are Tami River Rainbowfish and Lake Ifaten Rainbowfish.

This species was believed to have been first discovered by an expedition in the early 1950’s, found in a body of water thought to be an extension of the Tami River. However the initial discovery was not verified by the the leader of the expedition, ichthyologist Marinus Boeseman, and this species has yet to be found in the Tami River since. Although the common name “Tami River Rainbowfish” is still used, its accuracy is disputed. .

In 2001 it collected by Heiko Bleher, a German explorer well-known for his discoveries of many new freshwater fish species. He found this species in an isolated crater lake, dubbed Lake Ifaten, located in the mountains near Lake Sentani in West Papua, and so it is also called the Lake Ifaten Rainbowfish. There are also more recent suggestions of it being found widespread in lakes and rivers around the Sentani Lake area.

The Millennium Rainbowfish looks very similar to the Red RainbowfishGlossolepis insicus but there are some characteristic differences. The scales of the Lake Ifaten Rainbowfish are smaller and arranged differently and it is smaller than the Red Rainbow. It also begins to attain its adult red coloration at about 3 months of age, rather than taking almost a year as the Red Rainbowfish does. But because of its similar appearance to the well-known Red Rainbow, and its geographic location being close to G. incisus, it has been given the scientific name G. pseudoincisus.

Not a lot is known about this fish in its natural habitat as the Indonesian government has strictly limited access to the area. There are ongoing negotiations to allow icthyologists to gain access and survey and study these and other native fish.

Presumably its habitat, behaviors and diet are similar to that of other rainbowfishes of the region. They would tend to congregate in groups around the margins of lakes where there is vegetation and bog type wood, as well as in areas where the water is sort of turbid and almost stagnant with a muddy bottom and very dense with vegetation. Rainbowfish are known to feed on on small crustaceans, insect larvae, and algae.

  • Scientific Name: Glossolepis pseudoincisus
  • Social Grouping: Groups – Presumably congregates in schools like other rainbow fishes.
  • IUCN Red List: DD – Data Deficient – Not much is known about their native habitat due to government restrictions.


The Millennium Rainbowfish is a slender and laterally compressed fish. Mature males have an arched back and narrow head. The eyes are large, the mouth is deeply forked, and two dorsal fins are present. At around three months of age, the males begin to develop a crimson body color that quickly deepens into a very intense blood-red. The body is accented with small, reflective silver scales which are spaced fairly evenly in rows (Unlike its similar looking relative, the Red RainbowfishG. insicus whose silver scales are larger and appear more randomly).

Millennium Rainbowfish or Tami River Rainbowfish
Millennium Rainbowfish
Photo Courtesy: Heiko Bleher

Males will display varying shades and intensities of red depending upon age, health, temperature, water quality, mood, and even rank in the school. Displaying males have the ability to “turn on” a brilliant neon orange stripe which serves as a breeding signal to females. Females and young males will be silvery brown. Some females will show faint vertical stripes around the middle of the body.

  • Size of fish – inches: 4.0 inches (10.16 cm)
  • Lifespan: 5 years – Can have a life span of 5 to 8 years when kept in a well maintained aquarium.

Fish Keeping Difficulty

The Millennium Rainbowfish are rather rare, only a very few companies are shipping these rainbowfish. There is so much controversy on their actual habitat that it is hard to say what is truly ideal. That being said, they reportedly have been found in widely varying habitats, so keeping them should not be too much of a challenge. Provide a good filtration system, use diligence with water changes, and water testing. If these basic needs met, they will easily thrive.

  • Aquarium Hardiness: Moderately hardy
  • Aquarist Experience Level: Intermediate

Foods and Feeding

Millennium Rainbowfish are omnivores that feed on on small crustaceans, insect larvae, and algae in their natural habitat. Because diet can affect coloration greatly, special consideration should be given to formulating a healthy balance. At least 50-75% of the diet should be a suitable flake or pellet food. The rest should be made up of a variety of live foods like bloodworms, tubifex worms, brine shrimp, and daphnia.

Some good live food options include white worms, blood worms, or brine shrimp. If these are unavailable, frozen (defrosted) substitutes would be fine. Specially prepared commercial foods that are sold as ‘color food’ will contain dyes like carotene which is advantageous to enhance their color. These fish should be fed 2-3 times a day and only what they can consume in less then 5 minutes.

  • Diet Type: Omnivore
  • Flake Food: Yes
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Some of Diet
  • Vegetable Food: Some of Diet
  • Meaty Food: Some of Diet
  • Feeding Frequency: Several feedings per day – Feed two to three times daily, but give them only what they can consume in less than 5 minutes.

Aquarium Care

Rainbowfish are not exceptionally difficult to care for provided their water is kept clean. At least 25 – 50% of the tank water should be replaced weekly, especially if the tank is densely stocked. The importance of partial water changes can not be overstated, as this is a deciding factor of body color.They are very active swimmers and also jumpers, so be sure the tank has a secure cover.

  • Water Changes: Weekly – Weekly water changes of 25 – 50%, depending on stocking density.

Aquarium Setup

The Millennium Rainbowfish is a high energy species which will swim laps around the aquarium tirelessly. Due to the high activity level of this fish, a school can only be supported in a tank at least 30 inches long and at least 35 gallons in capacity. Eventually adults will need a larger tank, with 60 gallons or more being reasonable. Additionally, the tank should be securely covered as these fish are skilled jumpers and will probably do so if given the opportunity. A quality canister filter will be best to maintain suitable water conditions. Powerheads should be used to create water movement through dense vegetation.

The Millennium Rainbowfish will do best and are most effectively displayed in tanks which simulate their natural habitat. A sandy substrate, dense vegetation, and bog wood all echo their native lake areas. As with most of the Rainbowfish species they are most at home in well planted aquariums. The tank should be planted in the sides and back, with a stretch of open water in the middle. Bogwood and rockwork are both beautiful additions to the rainbow fish tank, but take care to arrange them so they won’t collapse amid all the activity. Slightly cooler temperatures, around 70° F (21° C) will make more of the males display brighter colors.

  • Minimum Tank Size: 35 gal (132 L) – The longer the tank the better, due to their high activity level.
  • Suitable for Nano Tank: No
  • Substrate Type: Sand/Gravel Mix
  • Lighting Needs: Moderate – normal lighting
  • Temperature: 70.0 to 79.0° F (21.1 to 26.1&deg C) – Lower temperatures, closer to 70° F (21° C), encourage males to display brighter colors.
  • Range ph: 6.5-8.5
  • Hardness Range: 15 – 25 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: Middle – Millennium Rainbowfish are usually found in the upper or middle regions of the aquarium.

Social Behaviors

Millennium Rainbowfish require tank mates with a similar temperament and activity level. Choose similarly sized species that are playful and social but not aggressive. The easiest and one of the most visually impressive ways to do this is to form a geographical tank, and put the Millennium Rainbow in with its cousins.

If the Millennium Rainbowfish is kept with both other males and females, the males will occupy themselves by displaying their brightest and best red colors and flaring their fins at each other. When males are displaying, you may notice some chasing between rainbowfish, but this is rarely a concern unless a fish is injured, has nowhere to hide, or is constantly harassed (usually a result of one of the first two).

Millennium Rainbowfish are schooling fish and the ratio of males to females is very important to keep a reasonable peace among them. Although you can always keep single sex schools, the coloration is an entirely different experience in a breeding condition mixed sex school. Properly stocking rainbowfish is a little tricky so we include the following recommendation for stocking. Choose which type of school you want to keep and how many fish.

If you wish to keep…

  • 5 rainbowfish – Do not mix sexes
  • 6 rainbowfish – 3 males + 3 females
  • 7 rainbowfish – 3 males + 4 females
  • 8 rainbowfish – 3 males + 5 females
  • 9 rainbowfish – 4 males + 5 females
  • 10 rainbowfish – 5 males + 5 females
  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species – conspecifics: Yes – Groups of 6 or more are preferred.
    • Peaceful fish (): Safe – Similar size tank mates are best.
    • Semi-Aggressive (): Monitor
    • Aggressive (): Threat
    • Monitor – Rainbowfish are fast wild swimming fish that can make slower fish nervous and stressed.
    • Shrimps, Crabs, Snails: Safe – not aggressive
    • Plants: Safe

Sex: Sexual differences

Mature males will be redder in coloration and will have a highly arched back and narrow head.

Breeding / Reproduction

A breeding tank should be set up with a sponge filer and either many fine leaved plants or a spawning mop. A pair of healthy adult rainbowfish should be introduced. They should be conditioned with live foods and plant based foods. Remember, you are trying to emulate the bounty of the flood season so feed more and higher quality food than you normally would.

After the female has produced eggs, the male will display an amazing show of intense colors and direct the female to the spawning site by doing a “headstand” over it, the pair will spawn, and then rest. The spawning mop or plants should be removed and replaced after the spawning or the eggs will be eaten. The fish will repeat this daily for about as long as you allow it, with steadily decreasing numbers of eggs produced. The parents should be removed when egg numbers fall or when the females show signs of fatigue.

The fry will hatch after about a week and should be fed infusoria or a liquid fry food until they are able to eat small live foods. The fry are something of a challenge to raise until they are about two months old. The fry grow slowly and require clean water during the entire process.

A problem to be aware of is crossbreeding. Rainbowfish in the wild will not breed with fish of another species, even when presented the opportunity to do so. But for some reason, rainbowfish of the Melanotaeniidae family in the aquarium will interbreed, often with undesirable results. Somehow the fry of mismatched parents lose most of their coloration. Since many of these species are rare, it is desirable to keep the bloodlines distinct, or risk losing the beautiful coloration that nature has taken thousands of years to develop. See an overview of how to breed Rainbow fish in Breeding Freshwater Fish.

  • Ease of Breeding: Moderate

Fish Diseases

Rainbowfish are extremely hardy and disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won’t have to deal with health problems or disease. Remember anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance.

A good thing about rainbow fish is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your Rainbow fish the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. Stressed fish are more likely to acquire disease.

For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments. This is a great source for information on disease and treatments. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. Rainbow fish are very resilient.


The Millennium Rainbowfish, also sold as the Tami River Rainbowfish or Lake Ifaten Rainbowfish, is only imported by a handful of companies, making it extremely rare in captivity.This fish is usually moderate priced, though a bit more costly than some of the other rainbow fish species.