The concentrations of plasma sex steroids and gonadal aromatase during controlled sex differentiation in grey mullet, Mugil cephalus

The objective of the study was to investigate plasma levels of sex steroids and gonadal aromatase activity during the period of controlled sex differentiation in grey mullet, Mugil cephalus. Six-month-old juvenile grey mullet were divided into three groups, control (n = 100), ethynyloestradiol (EE2, n=100) and 17 alpha-methyltestosterone ((17 alpha-MT, n=100), respectively. EE2 and 17 alpha-MT groups were fed diets containing 20 mg EE2 and 20 mg 17 alpha-MT/kg of feed, respectively, for 4 months (from June 25 to October 25, 1993). The majority of control fish (70%) were still at the undifferentiated stage after 4 months of experiment. By contrast, after 2 months of EE2 and 4-5 months of 17 alpha-MT treatments, all the fish had differentiated into females and males, respectively. Plasma testosterone (T) remained low over the first 4-month period and gradually increased later in the control group. Plasma T was significantly higher in the EE2 group in August after 2 months of treatment and in 17 alpha-MT group in October after 4 months of treatment compared to the controls. Low levels of plasma oestradiol-17 beta (E-2) (<100 pg/ml) were observed in all three groups during the experimental period. Plasma 11-ketotestosterone (11-KT) levels were lower in the EE2 group than in the other two groups. However, gradual increases of plasma 11-KT levels were observed in all three groups during the experimental period. Gonadal aromatase activity in the EE2 group was significantly higher than in the 17 alpha-MT and control groups from July to November. These data indicate that the concentrations of plasma T and gonadal aromatase activity are closely correlated with the development of controlled sex differentiation in grey mullet. (C) 1999 Elsevier Science B.V. All rights reserved.