Melanotaenia mairasi (male) - photo© Laurent Pouyaud

Melanotaenia mairasi

Allen & Hadiaty, 2011
Lake Furnusu Rainbowfish

Species Summary
Melanotaenia mairasi was described on the basis of 22 specimens, 12.1-54.2 mm SL, collected in November 2010 from Lake Furnusu in the Bird's Neck region of Kaimana Regency, West Papua Province, Indonesia. It is closely related to M. ogilbyi from central-southern New Guinea (southeastern Papua Province, Indonesia). The two species share similar meristic and morphological features as well as general colour patterns. The body of the males are a brownish colour dorsally and white ventrally, with a mid-lateral blackish stripe from the eye to the caudal-fin base. They have a narrow red stripe between each scale row of the body and orange scale margins. The dorsal and anal fins are a dusky-grey colour with red-orange margins, and a red caudal fin. Females are similarly coloured except the second dorsal and caudal fins are pale yellow, while the remaining fins are translucent to whitish.

The new species is named mairasi with reference to the tribal name of the traditional land owners of the type locality.

Distribution & Habitat
Melanotaenia mairasi is currently known only from the type locality, Lake Furnusu, which lies approximately 15 km northeast of Kaimana, West Papua Province. The lake is situated at an elevation of 15 m and is only about 1.5 km from the sea, but the two are separated from it by a steep ridge that rises to an altitude of about 500-550 m. The lake occupies a scenic basin that is approximately 5 km long and 1 to 2 km wide. It is completely surrounded by steep ridges without any connection to the nearby sea. Drainage appears to be subterranean, which is typical for other lakes in this region (e.g. Triton Lakes, lying 40 km to the southwest) that consists of rugged limestone karst. Except for the holotype, only juveniles were collected, but adult fish were seen among dense vegetation at depths below 2 to 3 m. Four other species provisionally identified as Neosilurus brevidorsalis, Craterocephalus fistularis, Mogurnda (new species), and Oxyeleotris nullipora were present in the lake.

Melanotaenia mairasi (female) - photo© Renny Hadiaty

The new species is closely related to Melanotaenia ogilbyi, whose nearest known population lies approximately 350 km southeast in the Timika region of Papua Province. Both species have similar meristic and morphometric features and similar colour patterns characterised by red stripes between the scale rows and a blackish midlateral stripe. However, there is a notable difference in the number of gill rakers on the lower limb of the first gill arch, 15-17 for M. mairasi and 10 or 11 for M. ogilbyi. The count for M. mairasi is the highest among the "maccullochi" species group. The present comparison of these species is somewhat restricted due to the lack of mature male specimens of M. mairasi and there remains a good possibility that additional differences may be evident when more specimens are available. The species is also similar in appearance to Melanotaenia sylvatica from the Lakekamu drainage of Papua New Guinea, but the latter has fewer gill rakers on the lower limb of the first gill arch (12 or 13), and usually fewer soft anal rays (16 or 17 compared with 18 or 19 in M. mairasi). There is also a modal difference in the number of pectoral rays with 12 or 13 (about 50% with each count) rays in M. sylvatica compared to 13 or 14 rays (about 63% with 14) in M. mairasi.

Allen G.R. & R.K. Hadiaty (2011) A New Species of Rainbowfish (Melanotaeniidae) from western New Guinea (West Papua Province, Indonesia). Fishes of Sahul 25(1): 602-607.

Adrian R. Tappin
Updated October, 2015

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