abstract:The cutlassfish, Trichiurus lepturus, has a worldwide distribution and shows morphotypic variation among regions. We investigated genetic variation within and among populations of T. lepturus from Taiwanese waters. We surveyed 636 bp (base pairs) of mitochondrial DNA (mtDNA) cytochrome (cyt) b from 99 individuals collected at eight locations. Two different phylogenetic analysis software packages were utilized (MEGA version 2 and PHYLIP version 3.6a2), using neighbour-joining (NJ) and maximum likelihood (ML) methods. The resulting topologies were identical. Both methods suggest the same conclusion, revealing four deep lineages. The genetic divergences among these four lineages compared with Trichiurus species-level divergences were low. Hence, this study supports that the high genetic variations of T. lepturus, collected from different cohorts in waters off Taiwan, originated from distinct spawning events.