EFFECTS OF SEX STEROID HORMONES ON SEXUAL SIZE DIMORPHISM IN YELLOW CATFISH (TACHYSURUS FULVIDRACO)

Sexual size dimorphism (SSD) is the evolutionary result of choosing different sizes for males and females, which is widely found in the animal kingdom. In the past few years, the yellow catfish (Tachysurus fulvidraco) has been studied in many fields as an important economic fish. Males grow faster and larger than females, but the mechanism is still unclear. In order to investigate the role of sex steroid hormones on the SSD in yellow catfish, we studied the effects of estrogen and androgen on the growth, gonadal development, energy acquisition, and allocation. Results showed that 17β-estradiol (E₂) administration significantly inhibited the growth of both males and females, and promoted energy allocation to the liver without significantly impacting food intake, suggesting that the growth suppression of E₂ are induced by different energy allocation rather than the acquisition of food intake. Treatment with synthetic androgen 17α-Methyltestosterone (MT) significantly increased food intake, promoted energy allocation to the liver, and reduced energy allocation to the ovary in females, which may explain the significantly increased growth in MT-treated group. These results only partially explain the different growth of the experiment group, and further study on the dimorphism may focus on the three aspects of energy absorption, distribution and consumption.