The Lake Kutubu Rainbowfish has the truest blues you will ever see on a freshwater fish!

The Lake Kutubu Rainbowfish Melanotaenia lacustris is a beautiful fish with an endearing personality. They are one of the larger rainbow fish, reaching almost 5 inches (12.5 cm) in length. They have constantly changing but always beautiful colors. Pairing these vibrant colors with an endearing personality makes the Lake Kutubu Rainbowfish one of the most amazing freshwater fish in the hobby.

With pristine water the Turquoise Rainbowfish are very 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 are also rugged and will adapt to many tank setups. Don’t be turned off when you see these fish in pet shops, as they are usually drab and gray. Once in the right stress free environment these fish will come to life and their colors jump right out at you.

This precious and rare species is in a very precarious position. This gem lives exclusively in Lake Kutubu. Wild populations are being decimated by over harvesting and environmental destruction. Domestically, this unfortunate fish is being bred recklessly with other species, muddling the bloodlines of species which have taken nature thousands of years of selective breeding to develop their beautiful colors. The World Wildlife Fund and other conservation groups have stepped in to make sure Lake Kutubu and its inhabitants are preserved.

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: Melanotaenia
  • Species: lacustris
Lake Kutubu Rainbowfish – Quick Aquarium Care
  • Aquarist Experience Level: Intermediate
  • Size of fish – inches: 4.9 inches (12.47 cm)
  • Minimum Tank Size: 30 gal (114 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 Lake Kutubu Rainbowfish Melanotaenia lacustris was described by Munro in 1964. Other common names it is known by are Turquoise Rainbowfish and Blue Rainbowfish. This fish is found only in Lake Kutubu and its outlet in southern Papua New Guinea situated in the Southern Highlands. Lake Kutubu was formed in a depression at 328 ft in the interior of the mountains and is the largest lake in Papua, New Guinea.

The water in that region is very clear and mostly fed from underground springs. Because it is supplied from underground and there is limestone the water passes through, it is alkaline and the pH is around 8.5-9. The lake is heavily populated with plants that can with stand these conditions. The Turquoise Rainbowfish are omnivorous, feeding on small crustaceans, insect larvae, and algae.

A weird thing happens every two years at Lake Kutubu that reduces this rainbow fish population, an up flow of dark water. Water comes up from the bottom of that lake which is called “the turning of the water”. When this happens it causes the water to become oxygen deficient, killing great numbers of fish. So combined with “the turning of the water”, gill nets, outboard motors, logging and oil drilling; the Lake Kutubu Rainbowfish is listed as “Vulnerable” on the IUCN Red List of Threatened Species. This lake is being looked at to be protected to help recover these fish.

So, combined with “the turning of the water”, gill nets, outboard motors, logging and oil drilling; the Lake Kutubu Rainbowfish is listed as “Vulnerable” on the IUCN Red List of Threatened Species.  This lake is being looked at to be protected to help recover these fish.

  • Scientific Name: Melanotaenia lacustris
  • Social Grouping: Groups – Congregates in schools like other rainbow fishes.
  • IUCN Red List: VU – Vulnerable – The World Wildlife Fund and other conservation groups have stepped in to make sure Lake Kutubu and its inhabitants are preserved.


The body type of the Lake Kutubu Rainbowfish is pretty consistent with that of its family. The body is long and it deepens as the fish ages. The head of an older male doesn’t follow the round contour lines of the body, instead it indents into a narrow triangular head. They have large eyes and paired dorsal fins.

Lake Kutubu Rainbowfish are capable of many colors but are perhaps best appreciated for their incredible blues, hence the common names Turquoise Rainbowfish and Blue Rainbowfish. These fish are usually cobalt blue to teal on top, and fade through green to silver or yellow on the bottom. Starting at the back of the tail, this fish usually has a thin cobalt blue stripe that disappears around the middle of the body.

Lake Kutubu Rainbowfish have the ability to change colors in a matter of seconds, and will display many different color patterns throughout the day. The fins have a slight bluish tinge, and may show black edges if the fish is in spawning condition.

  • Size of fish – inches: 4.9 inches (12.47 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 Lake Kutubu Rainbowfish are not very difficult to keep, however they like most rainbow fish they are very sensitive to water condition changes. But this can be taken care of with a good filtration system, diligence with water changes, and water testing. If the basic needs of these fish are met, they will easily thrive.

Getting their natural coloring to pop out is sometimes difficult in aquariums but not impossible. To get colors to their full potential the water must be pristine, and there needs to be a proper ratio of males to females. They are generally not picky eaters and will eat a variety of foods, but take caution not to overfeed.

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

Foods and Feeding

Lake Kutubu Rainbowfish are omnivores that feed on small crustaceans, insect larvae, and algae in its natural habitat. They should be fed a balanced diet, including live and processed foods to maintain good health. In captivity provide the Turquoise Rainbowfish with a high quality flake or pellet food. Purchase it in small amounts as the nutrients in these products quickly deteriorate past usefulness.

These rainbow fish also require a live food component in their diet. They should be treated with live foods like brine shrimp, bloodworms, and tubifex worms. These fish have small throats so they should be fed smaller foods 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. 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 Turquoise Rainbowfish are very active swimmers. It is also advisable to keep these rainbow fish in a tank at least 30 inches long and ideally 30 or more gallons. 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. An efficient filter and some water movement is needed for the male fish to develop their coloration. However, these rainbow fish need less current then most rainbow fish species.

The Lake Kutubo 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 the native Lake Kutubu area. As with most of the Rainbowfish species they 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 rainbowfish tank can be quite spectacular with the proper technique. Although these adaptable fish would certainly be happy in most conditions, the color is best displayed with a little planning. A dark substrate and backing on the tank contrasts with the colors and makes them more secure. 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.

  • Minimum Tank Size: 30 gal (114 L) – Adults will need a larger tank, of 60 gallons or more.
  • Suitable for Nano Tank: No
  • Substrate Type: Small Gravel
  • 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: 7.0-8.5
  • Hardness Range: 8 – 25 dGH
  • Brackish: No
  • Water Movement: Weak
  • Water Region: Middle – Lake Kutubu Rainbowfish spend most of their time in the middle and upper levels of the aquarium.

Social Behaviors

The Lake Kutubu Rainbowfish can adapt to life in a larger fish community aquarium, but is does exceptionally well in the geographical tank stocked with other rainbow fish. They should always be mixed with fish of a similar temperament and size range. These fish are by nature playful and boisterous. These behaviors can easily turn into violence and aggression with poorly chosen tank mates. These fish get larger then some community fish and their schooling movements can easily stress out other tank mates.

As they are schooling fish, 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. The following is what we believe to be the optimal stocking numbers for schooling rainbow fish. 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 – Can be shy and nervous if not in groups.
  • Compatible with:
    • Same species – conspecifics: Yes – Groups of 6 or more are preferred.
    • Peaceful fish (): Safe – Good tank mates consist of other Rainbowfish, characins, danios, barbs, gobies, and corydoras.
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Safe
    • Shrimps, Crabs, Snails: Safe – not aggressive
    • Plants: Safe

Sex: Sexual differences

Sexing is 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 more aggressive.

Breeding / Reproduction

A breeding tank should be set up with soft acidic water, a sponge filter, and most importantly either many fine leaved plants or a spawning mop. A group of Lake Kutubu Rainbowfish, in a two female to three male ratio should be introduced into the breeding tank. 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 a few days 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.

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 Lake Kutubu Rainbowfish, also sold as the Turquoise Rainbowfish or the Blue Rainbowfish, is usually available wherever rainbow fish are sold .This fish is usually moderate priced, though a bit more costly than some of the other rainbow fish species.