A majority of tuna caught by the commercial fisheries of the country is exported. The tuna population has already shown signs of overexploitation and decline worldwide. Therefore, the tuna should be properly studied and managed to ensure its sustainability. In this study, landmark-based geometric morphometrics was used to primarily generate body shape variations among male, female and between male and female tuna species.A total of 300 samples were collected in Zamboanga City, Western Mindanao, Philippines. Samples were utilized for imaging and land markings. Sexes of fish samples were determined by direct examination of gonads. Images were processed using geometric thin-plate grids (TPS) and relative warps (RW) software. The data generated from relative warp were subjected to PAST software to established shape variations displayed in the transformation of grids of the relative warps. Results revealed that there were shape variations between sexes and among species of tuna. The relative warp analysis showed that the males shape variations were found on the snout tip and dorsal fin. For females, the body shape variations were localized on snout tip and caudal peduncle. Three shape variations occurred both male and female E. affinis namely; the snout tip, dorsal extremity of the caudal fin, and interior of the anal fin. Discriminant Analysis was used to confirm shape variations between sexes of mackerel tuna species and revealed highly significant differences. However, there were also shared characteristics between sexes. A variation on snout tips can be attributed to their habitat and eating habits of both males and females. The shape variation among females can be accounted to the production of offspring. The shape differences of E. affinis were mostly affected by their behaviors and as well adaptation in the environment.

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