Studies on feminization,sex determination,and differentiation of the Southern catfish, <Emphasis Type="Italic">Silurus meridionalis</Emphasis>—a review |
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| Authors: | Z H Liu Y G Zhang D S Wang |
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| Institution: | (1) Key Laboratory of Eco-environments in Three Gorges Reservoir Region (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Science, Southwest University, Chongqing, 400715, China; |
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| Abstract: | 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., gthα, lhβ, and fshβ, 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. |
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