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

Author
item DAVIS, LORI - University Of Hawaii
item FOX, BRADLEY - University Of Hawaii
item Lim, Chhorn
item LERNER, DARREN - University Of Hawaii
item HIRANO, TETSUYA - University Of Hawaii
item GRAU, E. GORDON - University Of Hawaii

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2010
Publication Date: 6/1/2010
Citation: Davis, L.K., Fox, B.K., Lim, C.E., Lerner, D.T., Hirano, T., Grau, E. 2010. Effects of 11-ketotestosterone and fishmeal in the feed on growth of juvenile tilapia (Oreochromis mossambicus). Aquaculture. 305: 143-149.

Interpretive Summary: In fish, testosterone serves as a natural precursor for other sex steroids such as 11-ketotestosterone (11KT) in males and E2 in females, which play important physiological roles during testicular and ovarian development, respectively. It has been reported that feeding of 11KT increased the food conversion efficiency in juvenile carp. Juvenile male Nile tilapia displayed higher specific growth rate and lower feed conversion ratio than females. It was suggested that her plasma levels of 11KT may be involved in the higher metabolic capacity of males. However, there seems to be no report on long-term growth-promoting effects of 11KT in tilapia, or in any other teleost species. The present study attempted to determine whether the 11KT added to isonitrogenous and isocaloric diets, with or without fishmeal, possesses a growth-promoting effect in juvenile Mozambique tilapia. Juvenile tilapia (8 g average weight) were reared for 50 days with diets containing fishmeal or all-plant proteins, each with or without supplementation of 10 mg 11KT/kg. Fish fed fishmeal-based (FM) diets grew significantly faster than those fed all-plant (soybean meal-based, SM) diets. Addition of 11KT to the FM diet significantly improved growth, but no significant effect of 11KT was observed in fish fed SM diet. Males had 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 17ß- estradiol (E2) in females. Significant levels of vitellogenin (Vg) were found in male plasma. In both males and females, plasma Vg levels were significantly lower in fish fed SM diets than in fish fed FM diets. Our results indicate that addition of 11KT to the fishmeal-based diet stimulated growth, but with minimal effect on plasma levels of IGF-I, 11KT, E2 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.

Technical Abstract: The effects of 11-ketotestosterone (11KT) and dietary fishmeal on growth of tilapia (Oreochromis mossambicus) were examined. Juvenile tilapia, weighing about 8g, 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-1 (IGF-1) than did females; however, there was no consistent effect of fishmeal or 11KT on plasma IGF-1 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 17beta-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-1, 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.