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Abstract
Effects of storage temperature (ambient or refrigerated) and storage time on hormone-treated feed and the effectiveness of various feeds to reverse the sex of fry of Nile tilapia Oreochromis niloticus were studied. Seven feed storage regimes were tested, and fry were fed feed treated with 17α-methyltestosterone (MT) or a nontreated feed for 28 d. There was no significant difference among the stored MT-treated diets and ability to sex-reverse fry (P > 0.05). All treatments yielded 99–100% males. There were no significant differences in fry growth, survival, or feed conversion ratio (P > 0.05) among stored diets. Hormone analysis of feed showed that the initial concentration of hormone in the feed was 60.4 mg MT/kg feed, decreasing to 54.8 mg MT/kg feed after being stored under refrigeration for 2 months followed by 26 d at tropical ambient temperature (28 ± 1.5°C). Lipid analysis indicated that the feed was not rancid after storage for the period and conditions just described.