Effect of dietary administration of letrozole and tamoxifen on gonadal development, sex differentiation and biochemical changes in common carp (Cyprinus carpio L.).

The effect of letrozole and tamoxifen on the specific growth rate (SGR; % day(-1)), gonado-somatic index (GSI), total haemoglobin (g%), gonadal and serum protein as well as lipid, sex differentiation and 17 beta-oestradiol levels were studied in sexually undifferentiated Cyprinus carpio fingerlings 30 days post fertilisation (30 dpf) for 60 days. Results showed decreased GSI with tamoxifen treatment whereas letrozole increased it. There were reduced protein, lipid, triglyceride and cholesterol levels after treatment with tamoxifen and letrozole during gonadal development. Tamoxifen (200 mg kg(-1) feed) induced 82.5% masculinisation, whereas letrozole in the same dose produced 98.5% males. Gonadal 17b-oestradiol significantly declined from 86.0 +/- 1.41 pg per 100 mg (control) to 45.5 +/- 1.94 pg per 100 mg with tamoxifen and 36.0 +/- 0.72 pg per 100 mg with letrozole treatment. Similarly, serum 17b-oestradiol levels also decreased after tamoxifen and letrozole treatments. Testicular development in 37.8% of fish treated with tamoxifen and letrozole was found to be more advanced (spermatocytes) than in the control (spermatogonium); however, there was reduced ovarian growth and increased atresia. It was concluded that letrozole and tamoxifen both significantly affect sex differentiation and gonadal maturity in C. carpio leading to the production of sex-reversed males, yet the effect of letrozole was more potent.