Changes in the growth rate of Oreochromis mossambicus following treatment with the hormones, triiodothyronine and testosterone
1988
Howerton, R.D. | Okimoto, D.K. | Gray, E.G. (Hawaii Inst. of Marine Biology, Kaneohe, Hawaii (USA). Dept. of Zoology)
Studies were undertaken to assess the growth promoting activity of testosterone (MT) and triidothyronine (T3) in seawater-adapted tilapia. To determine the optimal dose of these hormones a dose-specific-growth response was characterized for both thyroid hormone and testosterone. T3 dose levels were 1, 5, 10 and 25 mg/kg of feed. MT doses employed were 0.1, 1, 5 and 10 mg/kg of feed. Hormones were dissolved in 50 ml of ethanol and the solution sprayed on the surface of feed pellets. The control diet was sprayed with ethanol only. Diets were fed to treatment groups of four hundred fish, at 4% of body weight, twice daily (total 8%) for 10 months. Biweekly random samples of ten fish per treatment were killed. Growth was inversely related to dosage in the thyroid treatment. The smallest dose (1 mg) resulted in the highest response, whereas the largest dose (25 mg) inhibited growth significantly. Growth and dosage were positively correlated in the MT treatment. All treatments resulted in increased growth rates with the highest dose (10 mg) being most effective. Fish from this treatment were more than twice the size of controls at the end of the treatment period. There were no significant differences in condition factor throughout treatment groups. Proximate analysis studies indicated that the hormone treatments produced no significant change in tissue water, protein or lipid content. Sex ratio in the T3 treatment was similar to the control group whereas in the MT treatment the altered sex ratio was dose dependent. The maximum dosage (10 mg) produced 94% males, while the minimum dosage (0.1 mg) did not significantly alter the sex ratio.
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