|Abstract: ||本論文研究莫三鼻吳郭魚苗的雄性比與成長。年齡5、10、20及30天的吳郭魚苗，暴露於水溫32、35及38℃，經5、10、20及30天。證實年齡5、10及20天吳郭魚苗，其雄性比及增重率有顯著差異。雄性比及增重率隨水溫增加而增加。暴露20及30天的魚苗，其雄性比顯著增加。暴露10及30天的魚苗，於水溫32、35及38℃之雄性比，分別為91.0％、82.3％及71.0％。雄吳郭魚苗的增重率為217-337.7％，雌吳郭魚的增重率為179-298.4％。本論文發現魚苗雄性轉變條件為於水溫32、35及38℃，年齡5及10天魚苗，暴露20及30天。雄性比(%)與水溫（C）、年齡（D）、暴露時間（T）以及年齡與暴露時間之交乘(DT)之關係式如下： 雄性比(%)=8.791+1.053C+0.455D-2.220T-0.007CD+0.090DT (R2=0.915)|
Tilapia is the third most important cultured fish group in the world, after carp and salmon (FAO, 2005). Tilapia culture is one of the fastest growing farming activities, with an average annual growth rate of 13.4% during 1970-2003 (FAO, 2005). The production of farmed tilapia increased from 383 thousand tones in 1990 to 1 million tones in 2003 with commercial value from 0.5 million US$ to 2 million US$ (FAO, 2005). Tilapia is widely cultured in about 100 countries in the tropical and subtropical regions (El-Sayed et al., 2005). Currently, almost 14 species of tilapia are being cultured in the world (Bardarch et al., 1972). The Java tilapia Oreochromis mossambicus is the second most important farmed tilapia species in the world after Nile tilapia Oreochromis niloticus, with 56 thousand tones of production and a value of 69 thousand US$ in 2003 (FAO, 2005). O. mossambicus inhabits in a wide range of environment; freshwater, blackish water and sea water (Chen, 1976). It can easily breed in ponds, with optimum temperature of 20-35℃ and salinity up to 35 o/oo (Morita et al., 2004). O. mossambicus can survive water temperature 10-39℃ and salinity up to 75 o/oo (Chen, 1976). A major limitation in the culture of O. mossambicus is over reproduction which leads to overcrowding and subsequently stunts the fish (Popper and Lichatowich, 1975; Bocek, 1993; Mair et al., 1995). Males have been reported to present better growth performances than females (Tonguyeni et al., 2002). In a period of 10 months from an initial weight of 5 to 10 g O. niloticus final weight was 302 g males and 210 g females, O. aureus was 259 g males and 119 g females and O. hornorum was 223 g males and 90 g females (Chen, 1990). Several studies have been conducted to solve the problem of over reproduction and slow growth, like use of predatory species. African cat fish Clarias gariepinus and Cichlasoma managuense have been used to reduce fingerling recruitment (Popper and Lichatowich, 1975; Dunseth and Bayne, 1978). Hand selection (Guerrero, 1975), hormone administration, through incorporation of 17α-methyltestosterone (MT) into diet (Guerrero, 1975; Gale et al., 1999), and hybridization of females of O. mossambicus crossed with males of O. hornorum (Bardarch et al., 1972) and female O. niloticus and male O. aureus or O. hornorum (Devlin and Nagahama, 2002) to produce all male offsprings have been developed. In addition, it is known that temperature affects the sex differentiation of tilapia (Mbahinzirek and Dabrowski, 1997; D’Cotta et al., 2001a). It is also known that O. aureus, fry at first 28 days of exogenous feeding produced 97.8% male sex ratio at 34℃ (Desprez and Melard, 1998) and O. niloticus fry at first 28 days of exogenous feeding produced 90% male sex ratio at 37℃ (Abucay et al, 1999). However, no information is available on the effects of temperature, tilapia fry stage and exposure period on male sex ratio. Therefore, the objective of this study was to determine the specific temperature, specific fry stage and specific number of days to be used in temperature sex differentiation for O. mossambicus.