The Boeseman’s Rainbowfish and has become a sensation due to its almost unreal coloration!

The Boeseman’s Rainbowfish Melanotaenia boesemani is a relatively new addition to the hobby but has quickly gained in popularity. It is an active and good sized rainbow fish, reaching up to 4.5 inches (11.5 cm). Looking at a mature male makes it easy to see why they are called Bicolor Rainbow fish. It is a beautiful blue-gray on the front half of the body and a vibrant orange-red on the back half.

Its coloration in a pet store is usually a dull steel gray and hardly seems worth purchasing. But a serious and patient aquarist can bring out unforgettable colors. The secret to good colors is to buy quality specimens, feed a varied diet, and above all keep up with frequent water changes and maintenance.

As with most rainbow fish, Boesemani Rainbowfish are excellent fish for beginners. They are hardy fish that are best kept in schools and so need a large aquarium, 150 gallons or more. But they will light up your tank with their beauty. If breeding is something you wanted to try, the Boeseman’s Rainbowfish is a great choice for that as well.

Being an endangered species, the Boeseman’s Rainbowfish deserves some special consideration. Wild populations were decimated by over harvesting and environmental destruction. Not only are harvesting practices usually damaging to the wild populations and environment, but they also upset the ecological balance in these regions. The government now has restricted the trade of these fish in an effort to prevent over-harvesting and to decrease their mortality.

Domestically, this unfortunate fish is being bred recklessly with other species, muddling the bloodlines of species. Nature has taken thousands of years of selective breeding to develop their beautiful colors. Please carefully consider purchasing responsibly bred rather than farmed fish.

Scientific Classification


Boeseman’s Rainbowfish – Quick Aquarium Care

Aquarist Experience Level:Beginner
Aquarium Hardiness:Moderately hardy
Minimum Tank Size:30 gal (114 L)
Size of fish – inches4.5 inches (11.43 cm)
Temperature:70.0 to 79.0° F (21.1 to 26.1&deg C)

Habitat: Distribution / Background

The Boeseman’s Rainbowfish Melanotaenia boesemani was described by Allen and Cross in 1980. The are found in Asia, more specifically in the Vogelkop Peninsula of Western New Guinea (formerly Irian Jaya). They are found only in the waters and tributaries of Lakes Ayamaru, Hain, and Aitinjo. They inhabit swampy shallow areas that are densely vegetated and feed on small crustaceans, insects, and some vegetation. Other common names they are known by include Bicolor Rainbow fish and Boesemani Rainbowfish.

The Boesemani Rainbowfish is listed on the IUCN red list as endangered due to over harvesting and environmental destruction. Trade restrictions of these fish have been put in place by the local government in an effort to prevent over-harvesting and to decrease their mortality.

  • Scientific Name: Melanotaenia boesemani
  • Social Grouping: Groups – Groups of 5 or more are preferred.
  • IUCN Red List: EN – Endangered – The Boeseman’s Rainbowfish is an endangered species.


The Boeseman’s Rainbowfish is the typical rainbow fish shape, long but deep, with an arched back and narrow head. They have relatively large eyes and two dorsal fins. The colors are very intense in well cared for and mature specimens. Male Boeseman’s Rainbowfish will reach 4.5 “(14 cm), females will be closer to 4” (10 cm). At around 2.5 inches in length, these fish will begin to develop their beautiful characteristic colors.

The back half of the fish will be a fiery red with orange and yellow highlights. The front half of the fish will be deep indigo blue or purple. The two colors come together in the middle with a few green or blackish vertical stripes. The female will have similar color distribution but will generally be less intensely colored and more noticeably silver. Fins should be opaque and yellow with a white outline.

Every fish has a slightly different distribution and so different intensity of colors, which is largely based on genetics. However age, health, water quality, and many other factors can and will impact their colors as well.<.p>

  • Size of fish – inches: 4.5 inches (11.43 cm)
  • Lifespan: 5 years – Can have a lifespan of 5 to 8 years when kept in a well maintained aquarium

Fish Keeping Difficulty

The naturally changing environments that these fish survive in, make it a moderately hardy fish for the new fish keeper. They are quite durable and normally can fight off most aquarium diseases.

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

Foods and Feeding

The Boeseman’s Rainbowfish are omnivores and are opportunistic feeders in the wild, with a natural diet of small crustaceans, insects, and some vegetation. In captivity they should be given a high-quality diet to encourage good coloration. A mix of live and processed foods is necessary for optimal health.

Buy processed foods in small amounts and frequently, as the nutritional value of these products quickly deteriorates past usefulness. Boeseman’s Rainbowfish relish live food like bloodworms, tubifex worms, water fleas, brine shrimp and the like. If these are unavailable, frozen (defrosted) substitutes would be fine.

  • 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. They are very active swimmers so a tank at least 30 inches long is necessary. They are 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

Rainbow fish will do best and are most effectively displayed in tanks which simulate their natural habitat. As with most of the rainbowfish species the Boeseman’s Rainbowfish are most at home in well planted aquariums. When you choose plants make sure to pick plant that can tolerate the hard, alkaline conditions preferred by this fish. They also need stretches of open swimming areas. A sandy substrate, dense vegetation, and bog wood all echo the native rivers of the Australian Rainbowfish.

A 30 gallon aquarium is minimum, but these are moderately large and very active swimmers so a tank size of 50 – 60 gallons or more is advisable. Of course a tank size of 150 gallons or more, will provide the best environment for a school of 5. Try, if possible, to plan for one or two hours of sunlight hitting the tank. This should be at a time when you can view the tank as the illumination will make the fish even more stunning. Additionally, the tank should be securely covered as these fish are skilled jumpers and will probably do so if given the opportunity. An efficient filter and good water movement are needed for the male fishes to develop their coloration.

  • Minimum Tank Size: 30 gal (114 L) – A tank of 50 to 60 gallons is advisable for these fairly large, active swimmers, and 150 gallon tank for a school.
  • Suitable for Nano Tank: Yes
  • Substrate Type: Sand/Gravel Mix
  • Lighting Needs: Moderate – normal lighting
  • Temperature: 70.0 to 79.0° F (21.1 to 26.1&deg C)
  • Breeding Temperature: 72.0° F
  • Range ph: 6.5-8.0
  • Hardness Range: 8 – 25 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: Middle – Boeseman’s Rainbowfish tend to gather in the open space of the aquarium, usually in the top or middle of the tank.

Social Behaviors

The Boeseman’s Rainbowfish do fine in a larger fish community aquarium of similarly sized fish, but do exceptionally well in a geographical tank stocked with other rainbowfish. Although generally non-aggressive, overly aggressive or very shy tank mates will make bullies out of them. Mix them with other playful but good natured fish for best results. 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).

Boeseman’s 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, you will see significantly better coloration if both genders are in the tank. 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

If putting your Rainbow fish in a community tank, provide ample hiding spots for these fish. With out the comfort of being able to find shelter it is unlikely to get the most of their coloration. In nature you will find them in schools under floating logs and plants when not swimming as a group, they need the same environment in the aquarium.

  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species – conspecifics: Yes – Groups of 5 or more preferred
    • Peaceful fish (): Safe
    • Semi-Aggressive (): Monitor
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Monitor – Rainbowfish are fast wild swimming fish that can make slower fish nervous.
    • Shrimps, Crabs, Snails: Safe – not aggressive
    • Plants: Safe

Sexual differences

Sexing is generally difficult at the young age at which the fish is usually sold, but mature males will be more colorful, have the arched back described above, and will often be the more territorial sex.

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 rainbow fish 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 males will display an amazing show of intense colors and direct the female to the spawning site, 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 a few days, with steadily decreasing numbers of eggs produced. The parents should be removed when egg numbers fall or if 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

The Boeseman’s Rainbowfish are moderately hardy but can have problems if the water is not well maintained. When water conditions are not at the right levels this fish will develop columnaris. These are long hair-like strings hanging off the mouths and sides of the fish. Fix the deficiencies in the water and the problem will clear right up.

Rainbowfish are very 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 Boeseman’s Rainbowfish, also sold as the Bicolor Rainbowfish or Boesemani Rainbowfish, is widely available in pet stores and online. This fish is usually moderate priced, though a bit more than some of the other rainbow fish species.



Featured Image Credit: Katerina Maksymenko, Shutterstock