Species, Freshwater fish, Rainbowfish

Lake Kutubu Rainbowfish (Melanotaenia lacustris)

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by Jason Matthews



The Lake Kutubu Rainbowfish is popular among fish hobbyists due to its striking colors and peaceful nature. In this article, we will look at the Lake Kutubu rainbowfish’s distinct characteristics and needs and why they make excellent additions to any community fish tank.

We cover everything from their origin to their behavior, tank conditions, tank mates, diet, breeding, and diseases. Prepare to dive into the world of Lake Kutubu rainbowfish and discover why they make excellent pet fish.


Scientific Name: Melanotaenia lacustris
Common Names: Lake kutubu rainbowfish
Life Expectancy: 5-8 years
Adult Size: 13 cm (5 inches)


HabitatFreshwater rivers and streams
OriginPapua New Guinea
Care LevelModerate
DietOmnivorous; requires a varied diet including high-quality flakes, pellets, live or frozen foods
Tank LevelMid to top level
Minimum Tank Size30 gallons
Water pH6.5-7.5
Water Temperature75-82°F (24-28°C)
Water HardnessSoft to moderately hard
LightingModerate to high
Tank MatesPeaceful community fish such as tetras, rasboras, and gouramis

Fun Fact Corner

One fun fact about Lake Kutubu rainbowfish is that they are known for their vibrant and shimmering colors, which can change based on their mood and surroundings. These fish can produce an iridescent sheen that glistens in the light, making them a spectacular sight.


The Lake Kutubu rainbowfish, Melanotaenia lacustris, is native to the pristine waters of Lake Kutubu in Papua New Guinea’s Southern Highlands. Scientists discovered and described this species in the early 1990s. They are known to inhabit the upper levels of the lake, where they can be found swimming in large schools among the aquatic vegetation. The Lake Kutubu rainbowfish’s origin highlights Papua New Guinea’s unique biodiversity and the importance of preserving its natural habitat. 

Appearance & Size

The Lake Kutubu rainbowfish body is elongated and slender, with a slightly arched back and a slightly pointed head. They have iridescent scales ranging from silver to red and everything in between. These fish’s vibrant coloration can change depending on their mood, lighting conditions, and location in the water column. 

One of its most distinguishing features is the lateral stripe that runs from the gill cover to the tail of the Lake Kutubu rainbowfish. This stripe, usually bright blue or green, can help distinguish the species from other rainbowfish.

The Lake Kutubu rainbowfish is a relatively small species, with adult fish reaching a maximum size of approximately 13 centimeters  (5 inches) long.


The Lake Kutubu rainbowfish is sexually dimorphic, meaning that the species males and females look very different. The most noticeable distinction between males and females is coloration, with males being more vibrant and intense. Furthermore, the males of the species are slightly larger than the females.

Male Lake Kutubu rainbowfish have a more elongated and slender body shape than females, typically rounder. Furthermore, males have longer dorsal and anal fins, frequently used for courtship displays during breeding.

Another significant distinction between males and females of the species is their behavior. Male Lake Kutubu rainbowfish have been observed to be more territorial and aggressive toward one another, particularly during the breeding season. Conversely, females are more passive and social, often forming large schools in the wild.


The Lake Kutubu rainbowfish is known in the wild for being active and social, often forming large schools that swim and forage together. In the aquarium, Lake Kutubu rainbowfish are known for their peaceful and non-aggressive behavior towards other fish species.


Selecting peaceful, non-aggressive species of similar size and temperament as tankmates for Lake Kutubu rainbowfish is critical.

Here are some good tankmates for Lake Kutubu rainbowfish:

Tank conditions

The proper tank conditions are critical for the health and well-being of Lake Kutubu rainbowfish. These fish are native to Papua New Guinea’s slow-moving rivers and streams, where they are accustomed to a tropical climate with warm water temperatures and high humidity.They require a water temperature of 74-82°F (23-28°C) and a pH level of 6.0-7.5 in the aquarium. 

In terms of water quality, Lake Kutubu rainbowfish are relatively hardy fish that can tolerate a moderate water flow. However, they require high water filtration and regular water changes to maintain a clean and healthy environment. It’s recommended to perform a partial water change of 25-30% once every two weeks to keep the water quality in optimal condition.

Lake Kutubu rainbowfish are relatively small fish that do not require a large tank. A minimum tank size of 30 gallons is recommended for a small school of these fish. However, larger tanks are always preferable for larger groups or keeping multiple fish species together.

In terms of décor, Lake Kutubu rainbowfish prefer a natural and well-planted aquarium environment with plenty of hiding places and swimming space. Adding live plants, such as Java Fern or Anubias, can help provide a natural and attractive environment for these fish while also providing oxygenation and filtration benefits to the water.


The Lake Kutubu rainbowfish is an omnivore that consumes plant and animal matter. They feed on insects, small crustaceans, and algae in their natural habitat. They can be fed a diet of high-quality dry foods in the aquarium, such as flakes, pellets, and frozen or live foods.

To provide a more varied and nutritionally complete diet, a staple diet of high-quality dry food should be supplemented with small amounts of frozen or live foods, such as brine shrimp, daphnia, or bloodworms.

It is also important to avoid overfeeding, as this can lead to water quality problems and potential health issues for your fish. It is best to feed small amounts 2-3 times a day and only as much as your fish can consume in a few minutes.


Breeding Lake Kutubu rainbowfish is a rewarding experience for experienced aquarists. These fish are egg layers, and breeding them in the aquarium requires a peaceful and stable environment with proper water conditions and a suitable breeding pair.

To encourage breeding, provide the fish with a varied diet and stable water conditions, such as a pH of 6.0-7.0, a temperature of 76-82°F, and a water hardness of 10-15 dH. A well-planted tank with plenty of hiding places can also help to provide a suitable breeding environment.

When the female is ready to breed, she will lay eggs in a hiding place or on the leaves of aquatic plants. The eggs hatch in 2-3 days, and the fry can swim a few days later. Feeding the fry small live or frozen foods, such as brine shrimp, is critical to ensure proper nutrition.


When it comes to the health of Lake Kutubu rainbowfish, it is critical to ensure that their tank conditions are optimal to prevent disease outbreaks. These fish are susceptible to ich (white spot disease), fin rot, and bacterial infections. It’s critical to keep an eye on your rainbowfish’s health and to act quickly if any signs of illness appear. Regular water changes and good water quality can help to prevent disease outbreaks.

In addition, it’s a good idea to buy healthy, disease-free fish from a reputable source and to quarantine new fish before adding them to your tank to avoid disease transmission. If you suspect your fish is sick, consult a veterinarian specializing in aquatic species for an accurate diagnosis and treatment plan.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

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