Abstract:The gonadogenesis, the development and differentiation of larvae and juveniles from 1~214 days post hatching (dph) and 18-month-old female and male spotted sea bass (Lateolabrax maculatus) were studied. The relationship between the expression of sex-related genes (cyp11b and cyp19a1a) and sex in the process of gonadal differentiation was discussed. The results showed that at 30 dph [(1.28±0.10) cm], primordial germ cells (PGCs) were first observed around the peritoneal membrane at the front end of the mesorenic duct, indicating that the time before 30 dph was the critical period for PGCs to migrate to the genital ridge. At 55 dph [(2.45±0.19) cm], a pair of symmetrically distributed primitive gonads was observed, indicating that the primitive gonads of the juvenile spotted sea bass were formed between 30 and 55 dph [(1.28~2.45) cm]. Between 55~180 dph [(2.45~12.28) cm], the primordial gonads continued to grow and remained in an undifferentiated state. After 180 dph, the gonads began to differentiate; at 195 dph [(14.54±1.54) cm], we observed that the testis began to differentiate, while the ovary began to differentiate at 205 dph [(15.86±0.94) cm]. The anatomical differentiation of the gonads was earlier than the cytological differentiation in spotted sea bass. The gonad of 18-month-old spotted sea bass developed to stageⅡ. The expression level of the sex differentiation-related gene cyp19a1a in the ovary of spotted sea bass was higher than that of the contemporaneous testis, indicating that it played a key role in the differentiation and maintenance of the ovary. The expression level of cyp11b at stageⅡ testis of 18-month-old juveniles was significantly higher than in the contemporaneous ovary and stage Ⅰ testes, suggesting that it played a crucial part in the differentiation and maintenance of testes. The results not only enriched our understanding of the reproductive physiology of spotted sea bass, but also provided a scientific basis for the study of sex selection technology.
