When 4 mg of testosterone (T) per kg food was given to 1-year-old protandrous male black porgy Acanthopagrus schlegeli for 7 months, gonadosomatic index was significantly higher than when the dose was 0.5 mg kg-1 food. Both doses of T prolonged the spawning season, and increased the number of spermiating fish and milt volume. Sperm concentrations were similar in spermiating black porgy from the treated and control groups. Low levels of oestradiol-17β were observed during the experimental period while elevated levels of plasma T were observed only in March in both control and T-treated groups. Significantly higher levels of plasma 11-ketotestosterone (11-KT) were observed in the 0.5- and 4.0-mg T-treated groups during the spawning season as compared to the control group. The present data suggest that both 0.5-and 4.0-mg T doses stimulate testicular weight, increase numbers of spermiating males and milt volume without affecting the sperm concentrations. Plasma 11-KT concentrations were elevated during T treatment and closely correlated with testicular development and spermiation.
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