Identification of a Nemacheilid loach from Kaptai Lake, Bangladesh using morphology and two molecular markers

The Nemacheilidae family of cypriniform fishes comprises more than 700 species inhabiting the rivers and streams throughout Eurasia. This family is considered one of the most taxonomically ambiguous, and recent research has shed light on its complexity. The Nemacheilid loaches collected during the survey of fish species in Kaptai Lake exhibited morphological ambiguity. The voucher specimens have incomplete lateral lines, including 10–12 round blotches. Molecular and morphological techniques were employed to identify and resolve the taxonomic confusion. The molecular study confirmed the species level of the specimens, showing an average similarity of 99.17 % with GenBank data of Acanthocobitis zonalternans. The highest level of genetic divergence recorded was 19.32 % between Paracanthocobitis botia, while proximity was noted with Paracanthocobitis abutwebi at 1 %. The phylogenetic tree based on maximum likelihood and maximum parsimony, constructed from the COI gene sequences of voucher specimens, reveals a monophyletic clade that includes the reference sequence of A. zonalternans. This analysis may also suggest incomplete lineage sorting with P. abutwebi. The Cytb gene sequences formed a distinct clade for the voucher specimens, indicating that they belong to the same species. Regarding molecular relatedness and morphological similarity voucher specimens conferred as A. zonalternans.