Abstract:he 5×3 two factor random animal experiment was conducted for 108 days to determine the effects of protein levels and satiation degrees on growth performance and immunity activity of juvenile Cynoglossus semilaevis Günther (with average initial weight of 110±25g) in the industrial culture condition with closed recirculation seawater. The trial fish were randomly allocated into 15 triplicated treatments,with five diets at protein levels of 43%，46%，49%，52%，56%(A E groups）and three satiation degrees of feeding（100%，90% and 80%, asⅠ和Ⅱ and Ⅲdegree）. The results indicated that: (1)the best weight gain were found in both the highest protein level and the highest satiation degree. Weight gain ratio in group E was significantly higher than the other groups (13.75%-50.16%),and that of degree Ⅰ was significant higher than degree Ⅱand Ⅲ (7.57% and 14.08%), respectively; higher protein efficiency ratio and the minimum mortality appeared in the intermediate protein level , mortality ratio of group C was lower than the others (50%-75%) the highest feed conversion ratio and protein efficiency ratio were present in the lowest satiation degree,for which degree Ⅲ was higher than the others (4.78% and 5.32%), respectively .(2) the intermediate protein level and the highest satiation degree were stimulative to enhancing SOD activity, group C was significantly higher than the other groups (4.2%-34.79%) degreeⅠwas significant higher than degree Ⅱ and Ⅲ (15.27% and 25.70%),respectively; the intermediate protein level and 90% satiation were good for promoting LZM activity, group C was significant higher than the other groups (4.61%-18.07%), degree Ⅱ was significant higher than degree Ⅰ and Ⅲ (12.03% and 4.58%), respectively; the intermediate and higher protein level and the highest satiation degree were stimulative to enhancing complement C3，C4 activity; (3) the protein level of feed for maximum growth of juvenile C. semilaevis Günther in the industrial culture condition was 56%, but for optimal immunity activity and protein efficiency ratio was 49%-52%.
