Description of a New Clariid Catfish, Clarias pseudonieuhofii from West Borneo (Siluriformes: Clariidae)

Clarias pseudonieuhofii sp. nov. is described from the Kapuas River in Western Borneo. Morphologically, the new species differs from all other Southeast Asian Clarias species (excepting C. nieuhofii) by an anguilliform body with a short and narrow head (head length 18.5%-21.1% standard length (SL); head width 12.7%-14.3% SL). Clarias pseudonieuhofii differs from C. nieuhofii by a shorter anal fin (anal fin length 56.0%-58.9% vs. 59.7%-66.8% SL), a longer pelvic fin (pelvic fin length 6.4%-7.5% vs. 3.8%-6.3% SL), and a shorter occipital process (occipital process length 4.6%-6.8% vs. 7.6%-13.8% head length). An allozyme study revealed that the locus, PGM*, is diagnostic between C. nieuhofii and the new species. The lack of heterozygous genotypes of this allozymic locus in the localities of sympatry where both species were caught together indicates that they cannot interbreed; this thus constitutes indirect proof of their complete species status.