In order to investigate the relationships among growth,nitrogen budget,water temperature and fish size of cobia,by using the principles and methods of fish bioenergetics,a laboratory experiment was carried out to study the effects of water temperature(21,27 and 33 ℃)and fish size(about 10,20,50 and 100 g)on growth and nitrogen budget,and furthermore,the growth models in relation to water temperature and fish size and the nitrogen budgets at different temperature and size treatments were established in this paper.The results showed that:(1)Growth of cobia was affected significantly by water temperature and fish size as well as their interaction.The fastest growth rate occurred for cobia with initial body weight about 10 g at 33 ℃ and the lowest growth rate occurred for cobia with initial body weight about 100 g at 21 ℃ within the experimental temperature and size ranges.(2)In a given size group for cobia,SGR increased with temperature.At a given temperature,SGR decreased with fish size,and the relationships between SGR and W could be described as power functions for cobia.By using multiple regression analysis,the model,LnSGR=a bLnW cT dT² eTLnW,provided a good fit to the data of specific growth rate(SGR),water temperature(T)and fish size(W).(3)Within the experimental water temperature and body size weight ranges,food nitrogen,feces nitrogen,excretion nitrogen and growth nitrogen of cobia were influenced significantly by water temperature and fish size,and increased with temperature but decreased with fish size.(4)Nitrogen budgets differed as water temperature and fish size changed,and were more sensitive to water temperature than to fish size.In a given size group the proportion of food nitrogen allocated to growth at 27 and 33 ℃ was much higher than that at 21 ℃,but contrary to the proportion of food nitrogen lost in excretion.At a given temperature the variation of nitrogen budgets among different size groups was small.(5)More than 68% of food nitrogen was lost in excretion.So it could be concluded that relatively low water temperature made an obviously depressed impact on cobia growth,and nitrogen excretion was the main way of nitrogen expenditure from food for cobia,and nitrogen budgets of cobia were relatively constant at 27-33 ℃ within the experimental temperature and size ranges.