Key Laboratory of Eco-environments in Three Gorges Reservoir Region (Ministry of Education), School of Life Science, Southwest University, Chongqing 400715, China.
Fish Physiol Biochem. 2010 Jun;36(2):223-35. doi: 10.1007/s10695-008-9281-7. Epub 2008 Nov 12.
The sex ratio of the feral Southern catfish was reported to be about 1:1, while the fish obtained by artificial fertilization were always female. Hence, we examined the possible influence of the micro-environment during artificial insemination (pH of the ovarian fluid and concentration of the semen) and early development (feed, hatching temperature, and water) on the sex ratio of Southern catfish fry. In order to examine the possibility of the occurrence of gynogenesis during artificial propagation, cytological observations on the insemination processes and the artificial induction of gynogenesis were also performed. However, no male fish were obtained even in these experiments, excluding the possibilities of these micro-environmental changes on catfish sex ratio and the occurrence of gynogenesis during artificial propagation. Female-to-male sex reversal was achieved by treatment with fadrozole (an aromatase inhibitor) and tamoxifen (an estrogen receptor antagonist). Histological analyses on the gonadal development of both female and induced male fish were subsequently performed. Moreover, several genes involved in sex differentiation, such as dmrt1, foxl2, and cyp19, and three subunits of gonadotropin (gth), i.e., gthalpha, lhbeta, and fshbeta, were isolated. Their expression patterns were studied under normal gonadal development and sex reversal conditions. The results revealed that dmrt1, foxl2, and cyp19a were closely related to catfish sex differentiation, and the gth subunits were possibly related to ovarian differentiation and oocyte development. Taken together, we hypothesized that estrogen was highly responsible for the ovarian differentiation and feminization of catfish fry under artificial propagation, although the mechanism involved remains elusive.
南方鲶的性比据报道约为 1:1，而人工授精获得的鱼总是雌性。因此，我们研究了人工授精期间（卵巢液的 pH 值和精液的浓度）和早期发育（饲料、孵化温度和水）的微环境对南方鲶鱼苗性比的可能影响。为了研究人工繁殖过程中雌核发育发生的可能性，还对授精过程和人工诱导雌核发育进行了细胞学观察。然而，即使在这些实验中也没有获得雄性鱼，排除了这些微环境变化对鲶鱼性比和人工繁殖过程中雌核发育发生的可能性。通过使用 fadrozole（芳香酶抑制剂）和 tamoxifen（雌激素受体拮抗剂）处理实现了雌鱼到雄鱼的性反转。随后对雌鱼和诱导雄鱼的性腺发育进行了组织学分析。此外，还分离了几个参与性别分化的基因，如 dmrt1、foxl2 和 cyp19，以及三种促性腺激素（GTH）亚基，即 gthalpha、lhbeta 和 fshbeta。研究了它们在正常性腺发育和性反转条件下的表达模式。结果表明，dmrt1、foxl2 和 cyp19a 与鲶鱼性别分化密切相关，GTH 亚基可能与卵巢分化和卵母细胞发育有关。综上所述，我们假设在人工繁殖过程中，雌激素高度负责鲶鱼苗的卵巢分化和雌性化，尽管涉及的机制仍不清楚。
