Phylogeography of Rarely Occurring Freshwater Fish Gongota Loach, Canthophrys gongota (Hamilton 1822) (Teleostei: Cobitidae) from the Ganga-Brahmaputra-Meghna River basins, with notes on Its Range Extension and Conservation Status

The Gongota loach, Canthophrys gongota (Hamilton 1822), is a rarely encountered freshwater fish species in the monotypic genus Canthophrys, within the family Cobitidae. It has a limited distribution within the Ganga, Brahmaputra and Meghna River systems of the Indian subcontinent. The discovery of C. gongota in the Ramganga River suggests that this species may be more widely distributed in the Ganga River basin of India than previously thought. In this study, we documented the molecular phylogeny of C. gongota, using mitochondrial DNA markers to explore population structure and historical dispersal patterns across its habitat. The cytochrome c oxidase subunit I (COI) gene sequences of C. gongota were compared with available GenBank sequences from Bangladesh, India, and Nepal. A total of 7 haplotypes were identified in C. gongota populations, along with one maternal ancestral haplotype present across all populations, except in the Meghna River Basin in Assam, India. The haplotype diversity (Hd) was 0. 0.335, and the nucleotide diversity (π) was 0. 00268. The analysis of molecular variance (AMOVA) revealed that 98.4% of the variation occurred between populations, while 1.56% was observed within populations. The pairwise F- Statistic distance (FST) between populations was 0. 0.984. Mismatch distribution analysis and the negative, significant Fu' s Fs values provided evidence for population expansion. On the other hand, phylogenetic tree analysis revealed that C. gongota populations were closely related and grouped into distinct clusters. These clusters may indicate a shared common ancestor or recent gene flow, likely influenced by geographic proximity or migration patterns. Moreover, we discussed C. gongota’s distribution across the globe and its conservation status. The findings of this study provide important insights into the genetic diversity of C. gongota, for conservation efforts, breeding programmes, evolutionary history, speciation events, and how environmental changes influenced it over geological time.