Differentiation and Development of External Sex Characteristics of Shrimp (Fenneropenaeus chinensis)

Abstract:

Fenneropenaeus chinensis is one of the prominent aquaculture shrimp species in China. To better understand its reproductive biology, here we investigated the sexual differentiation and development of the shrimp. The morphological changes of the female thelycum and the male petasma were observed. The larvae of F. chinensis collected from Yellow Sea Fisheries Research Institute (YSFRI) in Aprils of 2012 and 2013 were cultured in a circulating water system. The adult F. chinensis were purchased from aquatic produce market. The samples were fixed in Bouin’s solution for 16–24 h after being anesthetized with seawater saturated with Mg2SO4, and then stored in 70% ethanol at 4℃ for observation of external sexual development. The images were taken by Olympus CX22 LEDRFS1 microscope. It was found that the sexual differentiation of female shrimp started at 16 days post-larva (PL16). A subsidence appeared in the conuli on the ventral plate between the fourth and fifth pairs of pereopods in female shrimp, but no subsidence in the conuli was found in male shrimp. The valves that were components of thelycum appeared at the base of the fourth (anterior valve) and fifth pairs of pereopods (posterior valve) at PL54. At PL112, the form of anterior valve appeared to be similar to “epsilon type”. At PL124, the thelycum began to develop. Compared to the development of thelycum, the growth of petasma of male shrimps was late. The initial differentiation of endopodite on the first pair of pleopods was found at PL54, indicating the formation of male external genitalia. At PL106, petasma appeared to be similar to that of adults. The cannelure became obvious and periphery up folded, but the endopodite on the first pair of pleopods in female remained a willow-leaf shape.