Mitochondrial DNA reveals genetic diversity and population structure of Reba carp ( Cirrhinus reba ) across rivers and haors of Bangladesh

Reba carp, Cirrhinus reba, is an economically important endemic fish species in Bangladesh. A 758 bp fragment of the mitochondrial DNA control region (mtDNA) was analyzed to assess the genetic diversity, intraspecific genetic structure, and historical demography of C. reba from three wild populations in Bangladesh. Individual samples were collected from two rivers (the Padma and Karatoya) and one haor (Dingapota) basin in Bangladesh. A total of 38 haplotypes were detected among the 89 individuals analyzed, which included 56 substitutions. Analysis revealed that the haplotype diversity (h) of the Padma River population was high (0.961 ± 0.026), followed by the Karatoya River (0.749 ± 0.055) and Dingapota Haor (0.753 ± 0.059) populations. On the contrary, nucleotide diversity (π) was high in the Karatoya population (0.007 ± 0.004), followed by the Padma River (0.005 ± 0.003) and Dingapota Haor (0.003 ± 0.002) populations. Pairwise F ST comparisons and AMOVA results indicate that the Karatoya population was significantly different from the Padma and Dingapota Haor populations. However, a statistically insignificant difference was observed between the Padma River and Dingapota Haor populations. The minimum spanning tree showed two different clusters of haplotypes. Phylogenetic analysis also revealed two distinct clades, one of which was composed of haplotypes from Padma River and Dingapota Haor, and the other from the Karatoya River. Demographic analysis indicated that the Padma River and Dingapota Haor populations underwent recent population expansion, as evidenced by significantly negative Tajima's D and Fu's Fs values and mismatch distribution analyses. In contrast, the Karatoya River population exhibited signs of weaker expansion, indicated by a significant negative Tajima's D but a positive, non-significant Fu's Fs value. Evolutionary factors, species biology, and hydrological characteristics of water bodies can all contribute to the formation of a structured population. Present findings can provide baseline information for initiating management strategies for this commercially important species in Bangladesh.