Production of Male Oreochromis niloticus GET Excel Tilapia by Egg Immersion in Methyl Testosterone Hormone

The masculinization of Nile tilapia, Oreochromis niloticus, GET Excel strain was conducted through egg immersion in two concentrations of 17 α-methyltestosterone (500 and 1000µg L -1 ) at different immersion times (24, 48, 72 and 96 h). The effects of hormone concentration (HC) and immersion time (IT) on egg hatching rates, fry growth, survival and sex ratio were evaluated. Immersion time significantly influenced hatching with decreasing hatching rates at increasing IT. Highest hatching rate of 85% occurred after 24h IT regardless of HC. Low hatching rate of 63 to 65% was obtained at 96h IT. Survival rate of post-treated fry in the net enclosure was not significantly different among treatments. Higher growth occurred in 1000µg L -1 HC although not significantly different from the other treatment. Higher proportions of male juveniles were obtained with increasing HC especially at 1000µg L -1 (97-100%) across all IT. The interaction effect of HC x IT demonstrated that HC at 1000µg L -1 induced production of higher percentages of tilapia males. This implies that HC is a primary factor contributing to the high production of male population of O. niloticus. Cost and return analysis showed an inverse proportion of the return on investment (ROI) with immersion time. Highest average ROI was obtained in 500µg L -1 (55.32%) and 1000µg L -1 (55.25%) HC at 24h IT and lowest in 1000µg L -1 (28.50%) and 500µg L -1 (32.42%) HC at 96h IT. This study has identified the HC and IT of eggs that contributed to highest percentage of male production, a vital information in improving efficiency of all-male tilapia juvenile production to support the growing aquaculture of this important fish species.