Chilatherina pagwiensis

Allen & Unmack, 2012
Pagwi Rainbowfish

Species Summary
Chilatherina pagwiensis is a small stream dwelling species, growing to a length of about 7 to 8 cm. They were described by Gerald R. Allen and Peter J. Unmack in 2012 on the basis of 31 specimens, 20.5-6.1 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 Chilatherina 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 Chilatherina campsi. Likewise, the former species most frequently has 20-21 soft anal rays compared to 21-26 (most frequently 22-23) in Chilatherina campsi. Analysis of genetic relationships based on mitochondrial cytochrome b sequences indicates a close relationship between Chilatherina pagwiensis and the ancestor to Chilatherina axelrodi and Chilatherina campsi.

The body colour is overall pale-grey on upper back grading to white over most of body; diffuse greyish stripe on each scale row of back; fins generally reddish, except pectorals semi-translucent whitish. Chilatherina pagwiensis was found in the same habitat with Chilatherina fasciata, which is widely distributed in northern New Guinea. The two species are easily confused without microscopic examination of the dentition, especially specimens under about 60 mm SL. However, Chilatherina fasciata differs in having both vomerine and palatine teeth, and although counts of dorsal and anal soft rays overlap with those of Chilatherina pagwiensis, it tends to have higher counts, especially for the anal rays. There is also an apparent difference in maximum SL with Chilatherina fasciata attaining 105 mm versus less than 80 mm SL for Chilatherina pagwiensis.

Distribution & Habitat
Chilatherina pagwiensis is currently known only from a single creek in the vicinity of Pagwi village, Sepik River system, Papua New Guinea. There are different names for the same creek, Kuin and Huin and it remains unresolved as to which name is correct. It is the only creek which crosses the southern section of the Maprik-Pagwi road, once in its upper reaches and once in the lower reaches. Given it seems widespread within this creek it is likely to be found in similar habitats elsewhere in the Sepik drainage. The type locality consisted of a quiet pool in a small creek, flowing through secondary forest. The paratypes were collected to a depth of 1.8 metres over a rock and mud bottom in a slow-flowing stream in closed-canopy forest. The latter site is situated approximately 400 km upstream from the sea at an elevation of about 30 m above sea level.

Chilatherina pagwiensis is currently not available in the aquarium hobby.

Allen G.R. & P.J. Unmack (2012) A new species of Rainbowfish (Chilatherina: Melanotaeniidae), from the Sepik River System of Papua New Guinea. Aqua, International Journal of Ichthyology 18(4): 227-237.

Adrian R. Tappin
October, 2012

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Chilatherina pagwiensis