Melanotaenia japenensis - photo© Gerald Allen

Melanotaenia japenensis

Allen and Cross, 1980
Japen Rainbowfish

Species Summary
Melanotaenia japenensis have an overall mauve colouration with silvery reflections on the back and sides. There is a red-orange horizontal stripe between each scale row on the body. Males have red-orange dorsal, anal, and caudal fins. Growing to a length of around 11 cm, males are usually deeper bodied than females. Melanotaenia japenensis is closely related to M. affinis and M. vanheurni of northern New Guinea. These species possess similar colour patterns and have dorsal and anal soft fin ray counts which are relatively high for the genus. However, M. japenensis differs from M. affinis by having a higher anal ray count (26-28 vs. 18-24), and from M. vanheurni by having fewer soft dorsal rays (15-17 vs. 18-21 usually 19). In addition, the male holotype of M. japenensis has a deeper body compared to similar sized males of M. vanheurni.

Distribution & Habitat
Melanotaenia japenensis were collected from Yapen (=Japen) Island situated in Cenderawasih Bay (formerly Geelvink Bay) off the northern coast of West Papua. With an area of approximately 2424 km², it is a narrow, elongate (approximately 170 km long and up to 25 km wide) island with a central spine of mountains which rise to a maximum elevation of 1500 metres, and was once part of the New Guinea mainland. It is in fact an isolated continuation of the Van Rees Mountains of northern New Guinea. Presumably speciation of M. japenensis has occurred in relatively recent times as a result of the separation of Yapen Island from the mainland due to a post pleistocene rise in sea level.

M. japenensis is apparently restricted to Yapen Island. They were collected in rocky rainforest streams at lower elevations on the southern side of the island. Temperature and pH recorded at the collection sites were 24-28°C and 7.2-7.8. The island represents a continuation of a coastal mountain chain found on the nearby (30 km distance) New Guinea mainland and has a maximum elevation of 1500 m.

Melanotaenia japenensis is sometimes found with Chilatherina pricei, but seems to be more common in smaller, shaded tributaries, rather than the main channel.

Melanotaenia japenensis were first collected in May 1955 by M. Boeseman. Only two specimens had been collected. Gerald Allen discovered the undescribed specimens during a study visit at Leiden Museum in 1977. The original specimens were both females without any remaining trace of colour pattern.

David Price who does missionary work on Japen Island collected specimens for his own aquarium, but it is still unavailable in the general hobby. Named japenensis with reference to the Japen Island, the type locality and only known collection site for this species thus far.

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.

Adrian R. Tappin
Updated January, 2007

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Melanotaenia japenensis