2023-05-082023-05-082023-05-082022-01-14http://repositorio.ifam.edu.br/jspui/handle/4321/1191The Amazonian manatee (Trichechus inunguis) belongs to the order Sirenia and it is an endemic aquatic mammal of the Amazon basin. Several studies on the biology of this species have been developed, however, the morphological aspects of the male reproductive system are not described yet. Therefore, the aim of this study was to describe the histological characteristics of the testis and seminal vesicle of this species. Samples from the reproductive system of 11 Amazonian manatees of different age classes were used, previously fixed in 10% formalin and deposited at the Aquatic Mammals Laboratory/INPA. The material was morphologically evaluated, and fragments were processed by traditional histological techniques, stained with hematoxylin and eosin and analyzed by light microscopy. The sections were photographed and its structures evaluated for morphology and morphometry. In general, the morphology of the reproductive system of the male Amazonian manatee was similar to that reported for other sirenian species. Furthermore, it was possible to differentiate sexually mature and immature animals based on their morphological aspects. The data obtained also corroborate the estimated age of sexual maturity for the species. This is the first report of histological evaluation of testicle and seminal vesicle of Amazonian manatee and, based on the results obtained, further studies should be carried out in order to understand the morphological variations observed in the analyzed adult individuals. Keywords: Reproduction. Histology. Sirenians.Acesso AbertoReprodução. Histologia. Sirênios.CNPQ::CIENCIAS AGRARIAS::MEDICINA VETERINARIATrabalho de Conclusão de Curso