Prenatal Development of Gonads in Siamese Crocodile Embryos (Crocodylus siamensis)

Abstract

In crocodiles, differentaition of gonads to testis or ovary was influenced by incubation temperatures. To manipulate sexual outcome of the offspring, the information of gonadal development in terms of timing and stages of development is crucial. However, there has been no reports in Siamese crocodiles (Crocodylus siamensis), indigenous fresh water crocodiles of Thailand. This study aims to investigate gonadal development in Siamese crocodile embryos at 35, 48, 63 and 69 days of incubation which belonged to the second half of incubation. Microscopic study of gonad from Siamese crocodile embryos showed the presence of gonadal ridges in embryos at 35 days of incubation, Migration of primordial germ cells was found within gonads at day 35 of incubation and during the same period sex cords were developed. Bipotential gonads were detected at 48 days of incubation and sex cords extensively developed at 63 days and at 69 days of incubation. The data suggested that development of testis and ovary may occur after hatching. Expressions of sex steroid hormones and receptors for sex hormones in Siamese crocodile are needed to be elucidated.