| Abstract | Two experiments were conducted to study the nursing strategies of MT sex-reversed Tilapia (Oreochromis niloticus) fry, both through on-farm trials at Namsai Farm, Prachinburi province, Thailand and on campus trials at the Asian Institute of Technology. The first experiment consisted of two trials, the nursing stage trial was conducted in order to compare different feeding regimes, using on farm mixed diet containing fishmeal and ricebran 1:2, and determine their suitability for providing a high survival rate at a suitable market size. A pre-determined stocking density of 2,160/ m2 post treated fry in 5 m2 nylon hapas suspended in 1150 m2 fertilised earthen ponds for 90 days. The feeding regimes (% of body weight) over a 30 day period, adjusted at 15 day intervals, were 6:3:2, 3:3:2, 3:2:2, 3:2:1, 2:2:1and2:1:1. The mean final weights of fry were 1.46, 1.21, 1.02, 0.74, 0.65, and 0.78 g respectively. The mean final lengths were 4.7, 4.2, 4.1, 4.1, 3.7 and 3.5 cm respectively. There was a significant difference (p<0.05) between the survival rates of fry from feeding regimes 3:2:1 (94.2%) and 2:1:1 (76.2%). The feeding regimes which produced the most suitable fry according to market size at the optimal survival rate were 3:2:1 and 2:2:1. The growing stage trial was conducted to compare the subsequent growth performance of MT sex-reversed fry from nursing stage. One hundred fry were stocked in 5 m2 hapas and suspended in a fertilised earthen pond for 8 weeks without receiving supplementary feed. The mean final weight of fish were 14.6, 14.9, 14.4, 16.0, 15.8, and 15.3 g respectively with mean survival rates of 87.7%, 87.7%, 84.7%, 79.3%, 74.3%, and 80.3%. The difference between treatments were not significantly different for mean final weight, net yield and mean survival rate. The results from experiment 1 showed that controlling feed during nursing of MT sex reversed fry is possible and economically feasible in Thailand, without inhibiting subsequent fish growth. The second experiment was conducted to compare the effect of farm grading systems of post treated fry (size) and different duration of nursing (age) on subsequent grow-out performance of MT sex-reversed fry. Cages, 2.25 m2 were stocked with 30 MT sex-reversed fry suspended in fertilised earthen ponds. No significance difference was shown between fry of different sizes. Although no interaction was shown between the effects of size and age on subsequent fish growth but the results indicated that fry held for periods longer than 150 days tended to show a decrease in growth rate. The water quality both inside and out side the experimental units was within favourable limits of both experiments. |