Melanotaenia iris is most closely related to M. goldiei, a widely distributed species in southern New Guinea, but differs in colour pattern and having more soft rays in the second dorsal fin (17 to 20 versus 12 to 17, usually 14 to 16) and more scales covering the suboperculum-preoperculum (about 30 to 40 versus 15 to 25). The nature of the midlateral stripe also differs between the two species. It is continuous and uniformly broad along the middle of the side in M. iris, but in M. goldiei it is generally absent or very faint anteriorly over a space covering about 8-10 scales, the stripe then recommences below the soft dorsal fin origin, becoming broadest on the caudal peduncle.
Adult males are bluish on the upper back and white on the lower portion with a vivid dark blue stripe (about 2 scales wide) on the middle of the sides. There is also a series of narrow, red-orange stripes between each scale row on the upper and lower margin of the blue midlateral stripe and one in the middle of the stripe particularly prominent. Median fins dusky blue-grey with white outer margin; pelvic fins white; pectoral fins translucent. Live colours of the female are unknown.
Distribution & Habitat
Inhabits the upper tributaries of the Strickland River system in southwestern Papua New Guinea. The Strickland River is a major tributary of the Fly River.
Known only from five specimens collected by D. Gwyther in 1984 from the Logatyu River, a mountain tributary of the Strickland River near Wankipe, Papua New Guinea. Presently unknown in the aquarium hobby. The species was named iris (Latin: goddess of the rainbow) with reference to the common appellation for the family to which it belongs.
Allen G.R. (1987) Melanotaenia iris, a new freshwater rainbowfish (Melanotaeniidae) from Papua New Guinea with notes on the fish fauna in head waters. Japanese Journal of Ichthyology 34 (1): 15-20.
Allen G.R. (1991) Field guide to the freshwater fishes of New Guinea. Christensen Research Institute, Madang, Papua New Guinea.
Adrian R. Tappin
Updated December, 2008