The complete mitochondrial genome of Clarias nieuhofii collected from Phatthalung, Thailand (16,502 bp) was assembled and annotated. The study aimed to understand the mitochondrial genome composition, examine genetic divergence, and explore the phylogenetic relationships within and between populations of C. nieuhofii . The goal was also to contribute to the understanding of Sundaland biogeography and inform future conservation strategies. The circular mitogenome, which contained 13 protein‐coding genes (PCGs), two rRNAs, 22 tRNAs, and a control region (CR), had 28 genes encoded on the heavy strand, whereas NADH dehydrogenase subunit 6 ( ND6 ) and eight tRNAs were encoded on the light strand. The genome was AT‐biased (57.85%–57.87%), which is consistent with other Clarias species. DNA barcoding (cytochrome c oxidase subunit I COI and cytochrome b Cytb ) and species delimitation analyses were conducted to assess intra‐ and interspecific divergence. A positive COI barcoding gap (1.91%) but a negative Cytb gap (−6.94%) were observed. Delimitation tests variably split the three C. nieuhofii groups, with Cytb separating all groups and COI distinguishing Thai sequences (Group 3: Sumatra, Thailand) from those from Kalimantan (Group 1: Sumatra, Kalimantan). Phylogenetic and molecular analyses recovered three well‐supported, geographically structured clades (divergence ~18 million years ago MYA), in which Thai and Sumatran samples clustered together, and Kalimantan samples formed distinct clades. These results suggest cryptic diversity within C. nieuhofii , underscoring the biogeography of Sundaland and the need for broader sampling and region‐specific conservation.
Sornchai et al. (Thu,) studied this question.