Effects of 11-ketotestosterone and fishmeal in the feed on growth of juvenile tilapia ( Oreochromis mossambicus)

Abstract

The effects of 11-ketotestosterone (11KT) and dietary fishmeal on growth of tilapia ( Oreochromis mossambicus) were examined. Juvenile tilapia, weighing about 8 g, were reared for 50 days with isonitrogenous and isocaloric diets containing fishmeal or all plant proteins, each with or without supplementation of 11KT. Fish fed fishmeal-based (FM) diets grew significantly faster than those fed soybean meal-based (SM) diets. Addition of 11KT (10 mg/kg) to the FM diet significantly augmented growth, whereas no significant effect of 11KT was observed in fish fed SM diet. In accord with the accelerated growth, specific growth rates of fish fed FM diets were significantly greater than those of fish fed SM diets, although addition of 11KT to FM or SM diet had no effect on this parameter. Males showed significantly higher plasma levels of insulin-like growth factor-I (IGF-I) than did females; however, there was no consistent effect of fishmeal or 11KT on plasma IGF-I levels within each sex. Plasma levels of 11KT were significantly higher in males than in females. In males, plasma 11KT levels were significantly higher in fish fed FM diets than in those fed SM diet. No significant effect of fishmeal or 11KT was observed on plasma levels of 11KT or 17β-estradiol (E 2) in females. Low but significant levels of vitellogenin (Vg) were found in male plasma. Plasma Vg levels were significantly lower in fish fed SM diets than in fish fed FM diets in both males and females. These results indicate that addition of 11KT to the fishmeal-based diet stimulated growth, minimally affecting plasma levels of IGF-I, 11KT, E 2 and Vg. The absence of effect of 11KT in fish fed the soybean meal-based diet may indicate that the estrogenic activities or some components in the SM diet are likely to interfere with the growth-promoting effects of 11KT.