A new species of Rainbowfish (Chilatherina: Melanotaeniidae), from the Sepik River System of Papua New Guinea

A new species of rainbowfish, Chilatherina pagwiensis, is described on the basis of 31 specimens, 20.5-76.1 mm SL, collected from a tributary of the Sepik River near Pagwi village, East Sepik Province, Papua New Guinea. Morphologically it is closely allied to C. campsi, an inhabitant of mainly hilly or mountainous terrain in the Markham, Ramu, and Sepik river systems of northern Papua New Guinea and the Purari system, south of the Central Dividing Range. Both species are characterised by the absence of vomerine and palatine teeth, and males and females are relatively slender (greatest body depth 23.7-32.3 % SL) compared to most other family members. However, the two species exhibit pronounced modal differences in soft dorsal and anal rays. Chilatherina pagwiensis usually has 10-12 soft dorsal rays compared to usual counts of 13-15 in C. campsi. Likewise, the former species most frequently has 20-21 soft anal rays compared to 21-26 (most frequently 22-23) in C. campsi. Analysis of genetic relationships based on mitochondrial cytochrome b sequences indicates a close relationship between C. pagwiensis and the ancestor to C. axelrodi and C. campsi. The mean p-distance of C. pagwiensis to its relatives was 2.8 and 3.8% respectively, which are similar to values recorded between other rainbowfish sister species.