Male M. boesemani
In 1954, an expedition to Dutch New Guinea, now West Papua, sponsored by the Rijks Museum of Natural History in the Netherlands, and headed by Dutch ichthyologist Dr. Marinus Boeseman, collected several specimens of rainbowfishes from the family Melanotaeniidae (Mel-a-no-tay-nee-id-ee).
Twenty six years later, in 1980, Gerald Allen and Norbert Cross of the Western Australian Museum reviewed those specimens and classified four new species, including the subject of this article, Melanotaenia boesemani, the Boesemani rainbowfish. A few years later, Allen and Cross traveled to West Papua and collected live specimens of M. boesemani and were then bred and distributed worldwide for the aquarium hobby.
Today, we enjoy the bright colors, and active, peaceful behavior of M. boesemani in our freshwater community aquariums. Many commercially available specimens are captive bred, and can be easily found at most local fish stores.
M. boesemani are unique from other rainbowfishes in their distinct coloration and tall scale shape. Unlike other members of the family Melanotaeniidae, Male M. boesemani have a bicolor pattern. They display cool blues and blue-greens on their anterior (front) half and warm yellows and orange-reds on their posterior (back) half.
Female M. boesemani differ from males in their narrower body depth and shorter dorsal fin rays. Their coloration is less bisected. Dominant females have similar colors to subordinate males, but most females are a single shade of duller blue-green to gray, or only have a faint yellow to their posterior half. They have distinct orange horizontal stripes along their flank that run in conjunction with each scale row. They also have a dark vertical stripe halfway down their side.
M. boesemani males can reach up to 4.5 inches, females 3.5 inches. They have a lifespan of 5 to 8 years depending on diet, water quality, and water temperature.
M. boesemani are endemic to the Ayamaru Lakes and surrounding marshes and streams on Bird’s Head Peninsula in West Papua, Indonesia. This is where they evolved and exist naturally. The lakes rest atop the Ayamaru Plateau, 350 meters above sea level. M. boesemani are known to the native peoples of this region as “sekiak” and “ikan rascado”, and are occasionally caught and dried for consumption (Boesemani 1956). They spend their lives amongst the densely vegetated, sandy, and muddy shallows of several of the lakes and marshes in the area (Boesemani 1956). These lakes are warm at a temperature between 78 and 80 degrees F. The pH has been reported throughout the region as 9.0 (Bleher 1995), 6.4 to 7.8 (de Vries, 1962), (Reeskamp 1959), and 6.4 to 6.5 (Boesemani 1963). General hardness was recorded at 5 dGH (Bleher 1995).
M. boesemani prefers a densely vegetative habitat with sunken wood, rocks, and a natural substrate. There should be ample open water as well. Only portions of the tank should be densely vegetated. As a smaller, shoaling fish, they are cautious of predators and heavy cover allows for bolder behavior. In the aquarium, you’ll want plenty of cover and ideally, a soft substrate. They are benthopelagic swimmers, meaning they spend most of their time all over the water column, but favor the lower strata over the water’s surface. M. boesemani are peaceful, but can show aggression toward females during spawning events. In these cases, plenty of vegetative cover will break up aggressive behavior.
Aquarium Water Parameters
M. boesemani are adaptive to alkalinity and general hardness. They are susceptible to changes in pH, dissolved oxygen, temperature, and water quality. They require pristine water with very low nitrogenous waste (ammonia, nitrite, nitrate).
pH should be stable and maintained between 6.5 and 7.8. In my experience with M. boesemani in a high tech planted tank, pH fluctuations between 6.4 and 7.0 in a 24 hour period as CO2 levels change does not have an adverse effect on their health.
Rainbowfish can be sensitive to dissolved oxygen levels. An aquarium with ample surface agitation, and medium flow from a filter should provide enough dissolved oxygen if the tank is not overstocked. Rapid breathing, gasping at the surface, and pale gill filaments can be signs of poor oxygen levels in the aquarium. You can remedy this by increasing surface agitation by using a bubbler setup, increasing the flow from your filter, or installing a circulation pump within the tank.
Alkalinity & General Hardness
Alkalinity should be maintained, stably, between 2.8 and 11 degrees of carbonate hardness (dKH), with 4-8 dKH being the optimal range. General hardness should be maintained, stably, between 2.8 and 14 degrees of general hardness (dGH), with 4-10 dGH being the optimal range. Rainbowfish are not known to be sensitive to alkalinity and general hardness and will adapt to levels at the minimum or maximum of this range, or even beyond. However, an alkalinity and general hardness above 11 and 14 respectively can interfere with other aspects of your aquarium’s chemistry, like pH and CO2 levels.
M. boesemani, like many fish, are poikilothermic (poy-key-low-therm-ic). This means their body temperature hovers around the temperature of their environment. Increasing the aquarium temperature beyond 80 degrees will result in higher metabolism, faster growth rates, shorter lifespans, and the need for more nutrient intake. Keeping their temperature between 78 and 80 degrees Fahrenheit is ideal.
Rainbowfish are known to dart about the aquarium frantically in response to sudden and intense increase in lighting. This can result in injury and fish jumping from the aquarium. Using dimmers, or turning the aquarium light on after the room is lit will help mitigate this response.
M. boesemani are known for their intense coloration. To achieve and maintain these vibrant colors, they must consume a proper diet. Rainbowfishes come from diverse habitats and their diet reflects that. They are considered opportunistic feeders, meaning they will eat almost anything available. The natural diet for most rainbowfishes, M. boesemani included, consist of live foods including aquatic vegetation, terrestrial insects, small aquatic crustaceans, insect larvae, worms, phytoplankton, zooplankton, detritus, and sometimes smaller fish. A majority of their natural diet consists of aquatic insects (35%), crustaceans (14.4%), and algae (8.5%) (Tappin 2010).
A proper diet in the aquarium will help these fish maintain their vibrant colors, growth, and ability to reproduce. It should consist of protein heavy foods with plenty of nutrients, minerals, and vitamins. A high quality flake or pellet food can provide additives like vitamins and minerals. The right flake or pellet food will also include some vegetative ingredients as well, like spirulina or chlorella. This should be supplemented with a frozen food like bloodworms, rotifers, copepods, daphnia or Mysis shrimp.
One or twice a week, I recommend adding a small slice of zucchini or cucumber to the aquarium. Rainbowfish are known to readily feed on these and they provide an array of nutrients that would otherwise be unavailable. Any shrimp, algae-eaters, and snails will also enjoy the addition.
You can also supply your tank with a separate formula of fish vitamins which helps maintain their color, immune system, and reproductive health. Regardless, feeding a high quality processed food with protein and vegetable matter, and a frozen or live food daily will keep your rainbow fish vibrant and healthy.
With their natural habitat quickly disappearing, responsibly breeding rainbowfishes is an important aspect of keeping this fish. Breeding them responsibly means occasionally sourcing genetic material from the wild and from other captive broods. To breed one genetic line over and over into itself results in amplification of genetic defects and specimens diminished in physical and aesthetic capacity.
There is a wealth of information on breeding rainbowfishes in captivity available; far more than I could ever cover in this article. For an in depth description of breeding rainbowfishes, I refer you to the extensive work of Adrian Tappin and his publication “Rainbowfishes ~ Their Care and Keeping in Captivity”.
Even if you don’t intend to breed your M. boesemani, they may display courtship and spawning behaviors. This comes with some natural aggressive behaviors. To minimize aggression from males during spawning, it is recommended to keep the sex ratio at 3 to 6, males to females. One male can become too aggressive toward females. With two males, one can overpower and dominate the other. Three males diminishes their aggression by spreading it over several individuals and prevents physical abuse of the females.
Breeding rainbowfishes in captivity cab be relatively easy and should be responsibly controlled with the right setup. You’ll probably see courtship and display events occurring naturally in your aquarium.
6.5 to 7.8
2.8 to 11.2 dKH
2.8 to 14 dGH
Medium to High
40+ US Gallons
Non-aggressive to all species
With over 10 genera and 360 species, there are a plethora of rainbowfishes to enjoy in the aquarium. They come in all shapes and sizes, each one as colorful as the last. If you’re interested in learning more about the two families of fish that make up the rainbowfishes, Melanotaeniidae and Pseudomugilidae, I highly recommend the heavily researched, highly detailed, utterly through, and well respected publication by Adrian Tappin, “Rainbowfishes ~ Their Care & Keeping in Captivity”. This free to download, print quality book offers detailed insight into every aspect of keeping rainbowfishes, including but not limited to: their wild distribution and habitat, how they are caught and shipped from the wild, every possible aspect of their aquarium care, breeding habits, diet, disease prevention, and a summary of over 100 species.
Allen, Gerald R. & N. J. Cross. 1980. Descriptions of five new rainbowfishes (Melanotaeniidae) from New Guinea. Records of the Western Australian Museum 8(3): 377-396.
Bleher, H. (1995) The Fish of the Century. Fishes of Sahul 9 (1): 385-391.
Boeseman M. (1956) The Lake Resources of Netherlands New Guinea. South Pacific Commission Quarterly Bulletin 6(1): 23-25.
Boeseman M. (1963) Notes on the fishes of Western New Guinea. Zoologische Mededelingen Leiden 38 (14): 221-242.
de Vries J. (1962) Review of Inland Fisheries in Netherlands New Guinea. South Pacific Commission Fisheries Technical Meeting (Noumea, 5 - 13 February 1962).
Tappin, Adrian R. (2010) Rainbowfishes ~ Their Care & Keeping in Captivity. Art Publications. Australia.