Melanotaenia ajamaruensis (male) - photo© Laurent Pouyaud

Melanotaenia ajamaruensis

Species Summary
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). Among the places he visited was Lake Sentani, Tami River, Biak Island, Lake Jamoer (Yamur), Wissel Lakes, Ajamaru Lakes, Lake Ajtinjo, Merauke and the Digul River. This collection included many rainbowfishes, but a thorough study of the collection or description of the fishes was never made by Boeseman.

As part of his preparation for the revision of the rainbowfish family, Gerald Allen studied the Boeseman 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.

From field notes it was stated that Melanotaenia ajamaruensis have a metallic blue to yellowish or green with orange and yellow longitudinal stripes and dark scale edges. The body is ovate and laterally compressed. Mature males have a higher first dorsal fin, which overlaps the origin of the second dorsal fin when depressed. They grow to a length of around 11 cm; males are usually deeper bodied than females. They were named ´ajamaruensis´ with reference to the Ajamaru Lakes, the type locality and only known collection site for this species at that time.

In 1980 Allen & Cross described M. ajamaruensis as a species of Melanotaenia with the following combination of characters: dorsal rays IV to VI, 15 to 19; anal rays I, 21 to 27; pectoral rays 13 to 15; horizontal scale rows 7 or 8; vertical scale rows 34 to 37; predorsal scales 13 to 16 preopercle scales 9 to 16; colour generally reddish-brown on back and anterior half of body grading to yellow or tan posteriorly with series of red-brown horizontal stripes on side, in life ground colour metallic blue to yellowish or green with yellow longitudinal stripes.

M. 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. M. ajamaruensis further differs from M. boesemani by being more slender, and by having the first dorsal fin origin in front (by about one half eye diameter) of the anal fin origin compared to the approximately even position of these fins in M. boesemani.

Melanotaenia ajamaruensis (female) - photo© Laurent Pouyaud

Distribution & Habitat
M. ajamaruensis is a lake and stream dwelling rainbowfish found in relatively clear alkaline water, with abundant aquatic vegetation. Museum specimens were collected in March 1955 by Marinus Boeseman and his companions in the Ajamaru Lakes, a complex of lakes on the Ajamaru River in the centre of the Vogelkop Peninsula at the western extremity of New Guinea. 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 a number of small freshwater lakes and associated marshes. The largest lake, Lake Ayamaru drains east via the other two lakes (Lake Hain and Lake Ajtinjo) into an upper tributary of the Kais River that eventually flows into the Ceram Sea to the south. Lake Uter is a very small lake situated at the headwaters of Lake Ajtinjo. 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.

The Ayamaru lakes originally contained a small number of fishes and most of these were of very small size and diversity. The Dutch introduced some larger fish species, such as Cyprinus carpio and labyrinth fishes into the lakes in the mid-1930s to provide new sources of animal protein. As early as 1938, Trichogaster pectoralis, Helostoma temminckii and Cyprinus carpio were introduced into Lake Ayamaru to supply the requirements of a Dutch military post in that area. Cyprinus carpio was introduced to the lake in 1938, 1951 and 1969. Tilapia were introduced in December 1958, the stocks having been obtained from a hatchery in Manokwari. Gambusia (affinis) was introduced in 1959 for malaria control.

Reeskamp (1961) reported that "The local natives benefited by the somewhat improved stocks of fish in the lake since the native species were apparently seriously depleted many year ago. Generally speaking, the methods of fishing are very primitive and there is considerable destruction of fish by poisons, locally known as "akar kajoe" or "akar boreh", derived from the Derris (Derris elliptica?). This system of fish poisoning seems to be increasing and must no doubt have disastrous results on the existing stocks and will inhibit any development unless it can be fully prevented. Very large numbers of fry are killed by the poison and it is certainly in the interests of the natives themselves that this practice should be prohibited." Reeskamp also recommended that plant-eating fish should be introduced into the lakes to utilise the vast quantities of submerged aquatic vegetation (The introduction of Osphronemus gouramy was unsuccessful). It is unquestionable that the local natives benefited by the somewhat improved fish stocks in the lake as the native species were apparently seriously depleted many year before.

Rainbowfishes reported from these lakes include M. ajamaruensis and M. boesemani. It is also possible that these species inhabit other areas on the Vogelkop Peninsula, but most of the region remains unsampled. Other species reported as occurring in the lakes and surrounding streams are Pseudomugil reticulatus, Glossogobius hoesei, Chaenogobius isaza, Arius spp. (one is cream-coloured and the other black) and Glossamia sp. There are apparently reliable reports that large eels also occur in the Ajtinjo Lake. Crayfish are abundant in the lakes. Two species have been observed, one of which attains about 5 cm in length and the other about 10 cm (Cherax holthuisi was collected by Boeseman in 1952 from the Kais River). Also, possibly three species of giant prawns (Macrobrachium), which local have named according to their colour: udang biru (blue), udang hitam (black), and udang putih (white, but occasionally with some reddish-orange). However, very little research has been carried out, and it is possible that other species occur in the lakes.

The waterplant Ceratophyllum demersum has been recorded from the lake and Eichhornia crassipes was introduced in 1980s, but it covered only a small part of the lake. Formerly there were two species of submerged macrophyte (species not reported), but these disappeared or became very scarce after the introduction of Cyprinus carpio. As a result, one small species of fish local known as 'bobok' was reported to have become extinct because of the disappearance of its habitat (the submerged macrophytes). Heiko Bleher reported that the lake is almost filled with aquatic plants; mainly Vallisneria, Ceratophyllum and Najas species.

Remarks
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 as M. boesemani. At the time it was thought that females of M. boesemani were M. ajamaruensis. The natural colours of M. ajamaruensis at the time remained unknown. The type specimens preserved in the Leiden museum were the only ones that had so far been collected.

In 2007, a number of surveys were conducted by the Papuan National Marine and Fisheries Research, the Academy of Fishery Sorong, and the Institut de recherche pour le développement (IRD) Jakarta in five bioregions of West Papua. During the survey some rainbowfish specimens were collected that were considered to fit the type specimens of M. ajamaruensis as described by Allen and Cross in 1980. They were collected in an upstream section of the Kaliwensi River, about 5 km west of Lake Ayamaru. The river was 10-15 metres wide; 1-3 metres deep. The water was clear and fast-flowing over gravel and boulders with no aquatic vegetation. Water conditions report were: Temperature 24.7°C; pH 7.88 and Conductivity 217 µS/cm.

This river is an old outlet to the western side of the lake, but does not flow into the lake. It is thought that it probably flowed into Lake Ayamaru some decades ago, but only connected today by subterranean outlets. There is no connection between the lake and the river and M. boesemani doesn't occur in the river. This is currently the only known location of M. ajamaruensis today and it is thought that they no longer exist in Lake Ajamaru. The colouration of M. ajamaruensis can be much more intense than that shown in the accompanying photograph; displaying a brilliant red to red-orange colour (L. Pouyaud 2009, pers. comm.).

Note: The interesting thing about M. ajamaruensis is their remarkable similarity with M. boesemani. Is it possible that specimens of M. ajamaruensis may have been mixed in with some of the early collections of M. boesemani from Lake Ayamaru over the years? Perhaps M. ajamaruensis never occurred in Lake Ajamaru in the first place? Melanotaenia ajamaruensis are currently not available in the aquarium hobby.

Literature
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. Pouyaud, L. (2009) Personal Communications.

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.

Pouyaud L. (2009) Personal Communications.

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.