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DOI : 10.17693/yunusae.v15i21957.235771 Viewed : 3465 - Downloaded : 1998 Sexual dimorphism in fishes is not always easily observable. There are some exemptions where the dimorphism is obvious. Males in some species, especially the ones that the egg development undergoes inside female body, have a specialized structure called gonopodium, which distinguishes the males from the females. The first anal fin-ray has become a probe like organ to channel semen into the female`s cloaca during mating. Another example of the clear sexual dimorphism is presence of stripes on the males of Aphenius, a cyprinid. These stripes do not exist on the females, at all. Besides these rare occurrences, some sexual morphological differentiation may take place in the adults of some fish during reproduction period. The best example of this situation is the males of trout for which the shape of the mouth changes and elongates to take almost the shape of a beak. Despite such limited examples sexual determination in fish needs a thorough examination of an expert eye and/or an autopsy of the reproductive organs of the specimens which usually means the death of the specimen. Cyphotilapia frontosa used in this study is a favorable aquarium fish belongs to Tilapia family. The head shape becomes a horn-like extension over the head in adult males. Investigation for sexual dimorphism was carried out on 27 specimens. They were analyzed using geometric morphometrics methods where landmarks are used to evaluate the shape of the fish which does not necessitate the death of the fish however autopsy was also carried out to ascertain the results. For geometric morphometrics analysis the pictures of fish were taken and they were digitized using landmarks to determine the shape differences statistically. As a result sexual shape variation in Cyphotilapia frontosa individuals were determined. Keywords : Cyphotilapia frontosa,sexual dimorphism,geometric morphometry