|Melanotaenia boesemani - photo© Gunther Schmida
Allen and Cross, 1980
The colour pattern of male Melanotaenia boesemani is completely different from most other rainbowfishes and show a half-and-half colouration when fully matured. The head and front portion of the body are a brilliant bluish-grey, sometimes almost blackish, with the fins and posterior half of the body largely bright orange-red. Between these two areas, or roughly just behind the pectoral fin, there are alternating light and dark vertical bars. Their wild colouration can fade somewhat in captivity, possibly due to something lacking in the diet, or from the nature of captivity itself. They may reach a maximum size of 12 cm, but are usually less than 10 cm.
Males are easily distinguished from females by their different colour and longer and more elongated dorsal fin rays, and are usually much deeper bodied than females. Females display a broad dark mid-lateral stripe accompanied by a series of narrow yellow or reddish-orange longitudinal stripes corresponding with each scale row that deepen or lighten according to mood. Mature, older females often show colouration similar to subordinate males, but are usually easily identified by a shallower body/chest depth and smaller, more rounded fin edges.
Melanotaenia boesemani was named in honour of Dr. Marinus Boeseman, the collector of the type specimens. According to labels accompanying the type specimens the native name for this species is 'sekiak' and 'ikan rascado'. Marinus Boeseman was born on June 22, 1916 in Enkhuizen, a small port on the Zuiderzee in Holland. After the untimely death of his father, Marinus, aged 11, his two elder sisters and his mother moved to Oegstgeest, a neighbour town of Leiden where he continued his primary and secondary education. In 1935 he entered Leiden University to study biology. On November 1, 1947 he was appointed curator of fishes at the Rijksmuseum van Natuurlijke Historie in Leiden, and held that position until his retirement on 30 June 1981. He died on July 14, 2006 at the age of 90
Distribution & Habitat
Melanotaenia boesemani are found mainly in Lake Ayamaru and a few surrounding tributaries, but also occurs in Lake Hain and Lake Aytinjo. The Ayamaru Lakes region is located about 120 km east-southeast of Sorong, at the headwaters of the Ayamaru River in a mountainous region of the Vogelkop Peninsula, West Papua. The region contains three small freshwater lakes and associated marshes. The largest lake, Lake Ayamaru drains east via the other two lakes (Lake Hain and Lake Aitinjo) into an upper tributary of the Kais River that eventually flows into the Ceram Sea to the south. The lakes are positioned centrally on the Ayamaru Plateau, a heavily karstified region. The average elevation of the plateau is reported as 350 metres above sea level. The Ayamaru Plateau extends for 20-30 km to the south and south-west of the lakes before giving way to a broad zone of relict alluvial landforms dissected by wide flooded river valleys.
Lake Ayamaru has an area of approximately 22 km² and is located in a rather flat terrain, at about 250 metres altitude. The lake has variable depths with clear water and abundant vegetation. In the wetter months (April-June) the lake can rise by up to 5 metres from its dry season level; it never dries out completely, but the shoreline recedes several hundred metres. It has a muddy bottom, and the sediments of the shores are reportedly white, either sand or kaolin clay. The lakes and streams have a pH of 6.4-7.8 (de Vries, 1962) and temperate 26-27°C. Heiko Bleher reported the water conditions as pH 9.0, hardness 5° dGH, and conductivity 145 mS/cm. When Marinus Boeseman collected his specimens, he reported a pH of 6.4-6.5.
In August 1959, G. A. Reeskamp surveyed the lakes with the objective of determining the potential fisheries of the lakes. He reported that the lakes were shallow and interconnected by channels that might perhaps be better termed as "broads". The three lakes average approximately 7 ft. (2.13m) in depth and drain in an easterly direction into the Kais River. During the rainy season the water level rises to approximately 9 ft. (2.74m) and at the dry season large areas of these broads become dry. The greatest depth was found close to the southern margin of the lakes where a basin about 60 ft. (18.28m) diameter was discovered with a depth of approximately 20 ft. (6.09m). The outstanding characteristic of the lakes was the clearness of the water. Owing to the clarity of the water there is complete light penetration to the bottom with the resultant abundant bottom flora of aquatic plants. Samples of the waterplants were stiff to the touch, indicating a high lime content. The pH of the water determined by Bromothymol-blue was recorded as 7.8. Fish in these lakes appeared to be extremely scarce in relation to the large area of available water. In the shallow creeks along the margins, however, one obtains an impression of the fairly rich fauna but in the open water few fish may be seen and in general the fish appear to remain in the shallow margins of the lakes where food such as water insects, snails, fish fry, etc., are more plentiful.
Boeseman described Lake Aytinjo as "... a widened river, flowing southeast, with a length of 4 km and strongly varying width with a maximum of about 350 m. At the north-western, end the principal river widens to become a lake which consists of two parts separated by considerable rapids and small cataracts; at the south-eastern end the lake abruptly stops, but a subterranean connection with the Kais River is supposed to exist here. The mountains at most places closely surround the lake which has steep and rocky shores, almost perpendicular at some places but elsewhere allowing some wider marshy banks. The water is clear, pH about 6.5, flowing rather strongly only at the narrower parts of the lake, including the upper reaches. The bottom is rocky, at most places covered with sand, stones or large rocks, but muddy at some places. Both the aquatic and terrestrial vegetation are dense, at least where the stony substratum allows growth."
|Melanotaenia boesemani [Lake Aytinjo female] - photo© Joël Felix
Melanotaenia boesemani were originally collected from Aitinjo Lake by Sten Bergman during the Swedish New Guinea Expedition 1948-1949. Specimens are maintained in the Swedish Museum of Natural History. From October 1954 through to May 1955 Marinus Boeseman took part in a collecting expedition for the 'Rijksmuseum van Natuurlijke Historie' to Netherlands New Guinea (West Papua) with L.D. Brongersma and L.B. Holthuis. His task was to provide a thorough knowledge of the fish fauna by intensively surveying as many rivers and lakes as possible in western New Guinea. This task was taken to heart and in a relatively short period many localities were visited, resulting in a rich collection for the museum in Leiden. Among the places he visited was Lake Sentani, Tami River, Biak Island, Lake Jamoer (Yamur), Wissel Lakes, Ajamaroe (Ayamaru) Lakes, Lake Aitinjo (Aytinjo), Merauke and the Digul River. This collection included many rainbowfishes, but a thorough study of this material and descriptions of all the new species was never made by Boeseman.
As part of his preparation for the revision of the rainbowfish family, Gerald Allen studied the Dutch collection of 1954-55 during 1975 and 1977. He discovered no less than four new rainbowfish species, which he described in 1980 together with Norbert Cross. These species were Melanotaenia boesemani, M. ajamaruensis, M. japenensis and Glossolepis pseudoincisus. M. boesemani and M. ajamaruensis were collected in March 1955 by Boeseman and his companions in the Ajamaru Lakes, a complex of lakes on the Ajamaru River in the centre of the Vogelkop Peninsula. Specimens of Melanotaenia boesemani was also found in Lake Aitinjo, 25 kilometres to the southeast of Ajamaru village and from 'Djitmau', about 3 km south of the Ajamaru Lakes. The specimens preserved in alcohol still showed the unusual colour pattern.
Melanotaenia boesemani is readily separable from M. ajamaruensis on the basis of soft ray counts for the second dorsal and anal fins. The former species has 10 to 14 (usually 12 or 13) dorsal rays and 17 to 23 (usually 18 to 21) anal rays compared with 15 to 19 (usually 15 to 17) and 21 to 27 (usually 22 to 24) for M. ajamaruensis. Although these species possess a similar colouration and general shape, the stripes on the sides tend to be more pronounced in M. ajamaruensis, particularly the mid-lateral one and the stripe just below it.
In November 1982, Gerry Allen had the opportunity to collect live specimens during a visit to the remote Vogelkop Peninsula. Heiko Bleher, a well-known aquarium fish collector, had accompanied Gerry Allen on the trip and was able to transport a number of live specimens captured during the expedition back to Europe, whereupon they were subsequently bred and distributed in the aquarium hobby. Some live specimens were also sent to Australia. In 1998, Heiko Bleher collected more live specimens of Melanotaenia boesemani from Aytinjo Lake and they too, have been distributed in the aquarium hobby.
Since its introduction to the aquarium hobby, Melanotaenia boesemani has steadily increased in popularity and today, it could be considered the most popular rainbowfish in the hobby. By 1989 Ayamaru villagers were catching so many live fish for the aquarium trade the species was on the brink of becoming endangered. An estimated 60,000 male rainbows were captured each month for shipment to Jakarta exporters. Eventually the Indonesian Government placed some controls on the industry (Polhemus 2004).
In 2007-2008, a number of surveys were conducted by the Papuan National Marine and Fisheries Research, the Academy of Fishery Sorong, and the Institute of Research for Development of France in five bioregions of West Papua. During these surveys Melanotaenia boesemani were collected from a small 3-4 metre wide tributary of Tiwit Creek, less than 1 km north of Lake Ayamaru. The water was clear and slow-flowing over gravel and boulders with patchy vegetation. Water condition reported were: Temperature 24.8°C; pH 7.24 and conductivity 252 µS/cm.
Allen, G. R. and N. J. Cross (1980). Description of Five New Rainbowfishes (Melanotaeniidae) from New Guinea. Records of the Western Australian Museum 8 (3): 377-96.
Boeseman, M. (1956). The Lake Resources of Netherlands New Guinea. South Pacific Commission Quarterly Bulletin 6(1): 23-25.
Boeseman, M. (1956). Fresh-water sawfishes and sharks in Netherlands New Guinea. Science 123: 222-223.
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).
Holthuis, L.B., (1956). Native fisheries of freshwater Crustacea in Netherlands New Guinea. Contributions to New Guinea Carcinology. I. - Nova Guinea (n. ser.) 7(2): 123-137.
Reeskamp, G.A. (1961). Report of a Preliminary Survey of the Ajamaroe Lakes, Netherlands New Guinea. Indo-Pacific Fisheries Council - Occasional Paper 61/12. Food and Agricultural Organization of the United Nations.
Adrian R. Tappin
Updated April, 2013