Abstract
Toxic metal pollutants in aquatic environments negatively affect the natural characteristics of water and living organisms. Herein, 254 and 232 specimens (8-14/month) of the fish Siganus rivulatus (Teleostei: Siganidae) were caught alive during four successive seasons in the Red Sea, Egypt, from a chronically polluted bay and from an unpolluted bay, respectively. In each bay, the monthly water temperature was recorded, and the seasonal concentrations of Cd and Pb were determined in the water and in the intestine, liver, and gonads of both fish sexes. In the polluted bay, Cd and Pb were found in significantly high concentrations in the water and in the fish's intestine, liver, and gonads, and the concentrations only significantly increased in the fish gonads during the spring (spawning season). In each bay, seasonal levels of sex steroid hormones (testosterone T, 17 beta-estradiol E-2, and progesterone P4) in both fish sexes were determined, and they only peaked in both sexes during the spring. In male fish, the serum levels of these hormones throughout the year were in the order T > E2 > P4, while in the females, they were in the order E2 > T > P4. Compared to those in the fish from the unpolluted bay, the levels of these hormones in the fish from the polluted bay were greatly altered. Our results strongly suggest that the serum levels of sex steroid hormones are sensitive biomarkers for detecting heavy metal pollutants in aquatic environments and their effect on fish reproduction.