Genetic diversity and morphological stasis in the Ceylon Snakehead, Channa orientalis (Teleostei: Channidae)

As the type species of the genus Channa, the identity of the pelvic-finless snakehead Channa orientalis Bloch is important to channid systematics. Although this name has been attached to a Sri Lankan species for the past 160 years, its vaguely specified type locality, ‘India Orientali’, has long cast doubt as to its origin. Here, based on a collection across its range in the island and analysis of the cytochrome c oxidase subunit 1 (cox1) barcoding gene, we show that the Sri Lankan pelvic-finless Channa is composed of two geographically discrete lineages separated by an uncorrected pairwise cox1 genetic distance of 6.9–8.1%. The minimum genetic distance between these two lineages and other species of the Gachua group of Channa is 5.1%. Despite their genetic divergence, the two lineages exhibit remarkable morphological stasis: they are indistinguishable from each other in external morphology. We argue that the type locality of C. orientalis is south-western Sri Lanka, to which the species is endemic. Channa orientalis is distinguished from other species of Channa by the absence of pelvic fins, adult coloration in life, dorsal- and anal-fin ray counts, number of vertebrae, and scale counts.