Abstract
This study describes the morphological and histological characteristics of the male reproductive system of the orange mud crab, Scylla olivacea (Herbst, 1796). Three maturation stages were determined on the basis of the vas deferens diameter, the gonad colour and the gonadosomatic index (GSI). Significant differences were observed in the GSI value as the crabs matured. All germ cells were present in the histological sections of the testes, and these decrease significantly in size as they progress from spermatogonia, spermatocytes, and spermatids to spermatozoa. Spermatophores are found in the anterior vas deferens (AVD) and median vas deferens (MVD) of all maturation stages but not in the posterior vas deferens (PVD), with a significantly smaller size in immature and maturing specimens. Thus, the classification of S. olivacea gonads into various maturation stages based solely on histological characteristics (i.e., the presence of spermatophores) is impossible. Therefore, the combination of both microscopic and macroscopic features is essential for determining the gonad maturation stages of male S. olivacea.