Genetic homogeneity in longtail tunaThunnus tonggol(Bleeker, 1851) from the northwest coast of India inferred from direct sequencing analysis of the mitochondrial DNA D-loop region

Longtail tuna Thunnus tonggol is a neritic species of the family Scombridae, having a confined coastal distribution to tropical and temperate waters of the Indo-Pacific region. In the present study, the population structure of longtail tuna was examined using sequence analysis of the mtDNA control region from two geographically distinct locations along the northwest coast of India. A 500 bp segment of the D-loop region was sequenced and analysed for 98 longtail tuna individuals. Analysis of population differentiation showed no significant genetic differentiation between the two sampling localities (ΦST = 0.005, P = 0.200). Results were further corroborated by a non-significant nearest-neighbour statistic (Snn = 0.489, P = 0.549). Phylogeographic analysis revealed two haplogroups, but there was no obvious phylogeographic pattern separating the samples of the two localities. The present study suggests a single panmictic population of longtail tuna in the northwest coastal waters of India.