Comparison of hormonally induced sex direction in two strains of Oreochromis niloticus (Trewavas)

Abstract

Two strains (Grey Tilapia -TG and Red Tilapia - TR) of Oreochromis niloticus (Trewavas) fry were fed with the androgen 17-a-methyltestosterone at 60 mg/kg feed. Hormone treatment resulted in the production of 97% males in the TG strain and 96% males in the TR strain. There was no significant difference (P < 0.05) in percentage sex direction in the two strains. Nucleated oocytes could be distinguished clearly from oogonia in fish weighing 2 g and above. Gonadal development however, commenced earlier in the TR strain group with nucleated oocytes being observed from fish of 2 g weight while fish from the grey tilapia group showed gonads with nucleated oocytes at 2.5 g weight. Indistinct gonads were observed from all groups except TG control group. The number of indistinct fish was significantly higher in the TR control group than all other groups.


JOURNAL OF AQUATIC SCIENCES Volume 16, Number 2, October 2001, pp. 147-149




KEY WORDS:

Sex reversal, Oreochromis niloticus, Strain, Hormones, Oocytes, Gonads