Abstract: Using the histological methods, the gonadal development, structures of gonad, spawning time and type of reproduction in Tribolodon brandti were studied. The testes of T.brandti have typical lobular structures, and can be divided into six developmental stages. According to the characteristics of the ovaries and the types of ovarian germ cells, the oogenesis process can also be divided into six developmental stages. The microscopic observation showed that the gonadal development of sexual mature T. brandti differentiated to stage III at the end of September, and stayed at the phase III in the winter period. While the gonadal development of immature juveniles age 2+ was at the phase Ⅱ and remained such stage during the winter period. In the late April and early May, gonadal development of sexual mature males differentiated to the phase V, but in the females it was until late May or early June that they reached to the developmental phase V. Taken together, gonadal development of the males was faster than that of the females. No significant difference was observed in the gonad development of 2-3-year-old juvenile cultured in either fresh water or weak alkali water environment. The body weight 2+-year-old group in the weak alkali water were significantly higher than that in the fresh water, but no significant difference was found between 3+-year-old groups reared in weak alkali environment and those in fresh water. Meanwhile, significant differences of body weight existed between females and males in the weak alkali as well as in the fresh water. In the gonad development cycle, the average condition factor of female and male ranged from 1.313 to 1.697. During the sexual cycle, the male gonad index began to rise significantly from the II period, while the female gonad index was significantly different among development periods, with the peak value of 14.22 in the period of V. The conclusion could be drawn that the gonadal development peak of T. brandti appears only once a year, the ovary is partial synchronic, and this species is iteroparous.

Key words: Tribolodon brandti, germ cells, gonadal development, sexual cycle, sexual maturity