Melanotaenia oktediensis (wild-caught) - photo© Neil Armstrong

Melanotaenia oktediensis

Species Summary
Melanotaenia oktediensis were initially collected by C.R. Boyden from the Ok Tedi River at Tabubil, Papua New Guinea during the Cambridge expedition in 1974. In 1975, Dr. Tyson Roberts collected them from the lower portion of Karamonge Creek, a tributary of the Ok Tedi River during an ichthyological survey of the Fly River and mistakenly identified them as Melanotaenia vanheurni, a species found in the Mamberamo basin, northern New Guinea. After examining specimens in the Zoologisch Museum, Amsterdam and the American Museum of Natural History, New York, Allen and Cross recognised them as a distinct species and named them Melanotaenia oktediensis after the Ok Tedi River. Melanotaenia oktediensis have a body colouration that is coppery brown above a prominent mid-lateral line and pale mauve to white below. In many species of rainbowfishes, males change colour during the spawning procedure. Melanotaenia oktediensis is no exception and the colour changes from deep orange to yellow and green. They may reach a maximum size of 12 cm, but usually less than 10 cm.

Distribution & Habitat
Melanotaenia oktediensis are found in the Ok Tedi River and its tributaries. The Ok Tedi is one of the main headwater streams of the upper Fly River system. Melanotaenia oktediensis is uncommon in the main river, which is mostly populated by Melanotaenia rubrostriata. The tributaries of the Ok Tedi River are generally cool, clear, relatively fast flowing rainforest streams with rocky bottoms. Water conditions reported from these habitats were temperature 17-24° Celsius, pH 7.3-8.7, hardness 20-80 mg/L CaCO³, and a high dissolved oxygen content of 6.9-10.0 mg/L.

The Ok Tedi River begins near the Hindenburg Wall, a 1000 metre limestone escarpment and flows to the south where it joins the Fly River downstream at D'Albertis Junction. The Ok Tedi rises in an area of rugged topography, where mountains rise to more than 3000 meters. The region is humid and tropical, with a natural vegetation of moss forest and upper montane (cloud) forest beyond. The region has a stable tropical temperature range from a minimum of 19°C to a maximum of 27°C. Extremes of 12°C and 39°C have been recorded.

Remarks
Live specimens were collected by Gerald Allen in 1982 from creeks near Tabubil and brought back to Australia, where they were bred and distributed in the hobby. They were later sent to Europe and Northern America, but they have never been readily available in the hobby.

Literature
Allen G.R. & N.J. Cross (1980) Descriptions of five new rainbowfishes (Melanotaeniidae) from New Guinea. Records of the Western Australian Museum 8 (3): 377-396.

Allen G.R. (1991) Field guide to the freshwater fishes of New Guinea. Christensen Research Institute, Madang, Papua New Guinea.

Boyden C.R., B.E. Brown, R.F. Drucker and S.J. Tutt (1975) Ok Tedi Environmental Study. Report of the 1974 Cambridge Expedition to the Western District Papua New Guinea.

Richards S.J. and N. Whitmore eds. (2015) A rapid biodiversity assessment of Papua New Guinea's Hindenburg Wall region. Wildlife Conservation Society Papua New Guinea Program. Goroka, PNG.

Adrian R. Tappin
Updated December, 2015