Effects Of Sex Steroid Hormones On Sexual Size Dimorphism In Yellow Catfish(Tachysurus Fulvidraco)

Sexual Size Dimorphism?SSD?,commonly displaying throughout the animal kingdom,is the evolutionary result of selection operating differently on the body size of males and females.Yellow catfish?Tachysurus fulvidraco?has been studied in a wide range of fields as an important economic fish during the past years.Males grow faster and larger than females,however,the mechanisms involved remain unclear.In order to investigate the roles 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 17?-estradiol?E₂?administration significantly inhibited the growth of males and females,and resulted in higher energy allocation to the liver while did not significantly influence food intake,suggesting that the growth suppression of E₂ are induced by different energy allocation rather than acquisition.Treatment with synthetic androgen 17?-Methyltestosterone?MT?significantly increased food intake,lead to more energy allocation to the liver,and reduced energy allocation to the ovary in females,which was probably the reason that growth was significantly increased in MT-treated group.We will further study the SSD from the aspects of energy acquisition,allocation,and expenditure because the observed results in the present work can only partly explain the different growth patterns of males and females.