Citation MacIntosh D, Singh TB, Little DC & Edwards P (1988) Growth and sexual development of 17 alpha testosterone and progesterone treated Nile tilapia (Oreochromis niloticus) reared in earthen ponds. In: Pullin R, Bhukaswan T, Tonguthai K & Maclean J (eds.) Second International Symposium on Tilapia in Aquaculture. ICLARM Conference Proceedings, 15. Manila, Philippines: Metro, pp. 457-463. http://agris.fao.org/agris-search/search/display.do?f=1991%2FPH%2FPH91012.xml%3BPH8912378
Abstract Swim-up fry (average weight, 14 mg) were obtained from Oreochromis niloticus (Chitralada strain) held in concrete tanks. In experiment 1 (1985), fry were fed diets treated with 17 alpha-methyltestosterone (MT) or progesterone at 60 mg/kg for 40 days. Control fish were fed untreated diet. Fingerlings (average weight, 2.86 g) were subsequently stocked at 1/square m. in earthen ponds receiving septic tank slurry at 150 kg COD/ha/day and fine rice bran as supplementary feed for about 5 months. In experiment 2 (1986), similar procedures were followed but the fry were fed MT at 40 mg/kg for 40 days and pond stocking rates of 1,3,5 and 7 fingerlings/sq. m were compared. Individual size, sex and stage of maturity were determined. In experiment 1, the average individual size was greatest in the MT-treated group (263 g), compared with the untreated (232 g) and progesterone-treated fish (189 g). The final size of fish in experiment 2 decreased significantly (P0.05) with density, from an average of 249 g at 1 fish/meter square average of 249 g at 1 fish/square meter to 94 g at 5/square meter; however those stocked at 7/square meter gave the highest total biomass and were not significantly smaller (P0.05, mean weight, 88g) than the fish stocked at 5/square meter. Sex could not be determined by external morphology alone, but sexing on gross gonadal structure agreed well with subsequent histological examination. The percentages of male fish were: MT-treated, over 93%; progesterone-treated, 72% and untreated, 57%. All treatments included fish at various stages of maturity, from undifferentiated to fully mature gonads. In MT-treated fish, females commonly showed abnormal enlarged ovaries: egg bound or distented with fluid. Some males, particularly those fed the higher level of hormone (60 mg/kg) showed some testicular degeneration which lowered GSI [gonadosomatic indices] values.
MacIntosh, Donald; Singh, T B; Little, David Colin; Edwards, Peter