Effects of eco-nutrition requirement of protein on Cynoglossus semilaevis Günther in industrial culture with seawater quality and digestive enzyme

The experiment was conducted to determine effects of protein levels and satiation degrees on juvenile Cynoglossus semilaevis Günther in industrial culture conditions with closed recirculation seawater.The 5×3 two-factor random animal experiment lasted for 108 days,total of 1125 fish［with initial weight(110±25) g］were randomly allotted into 15 treatments with triplicates,25 fish each replicate,5 protein levels diets(43%,46%,49%,52%,56%,with A-E),3 satiation degrees feeding(100%,90%,80%,withⅠ,Ⅱ and Ⅲ).Evaluated effects of different protein levels and satiation degrees on juvenile C.semilaevis growth performance,seawater environment factors and digestive enzyme.The primary results showed that:(1)As the protein level of feed and satiation degree increased,weight gain increased significantly(P<0.01),the best weight gain both in the highest protein level and the highest satiation degree.Weight gain ratio in group E was significantly higher than the other groups by 13.75%-50.16%,that in degree Ⅰ was 7.57% and 14.08% higher than degree Ⅱand Ⅲ .The best feed conversion ratio appeared in the highest protein level,which was significantly higher than the other groups by 6.25%-27.44%(P<0.05),but satiation degree didn’t have such significant impact on FCR as protein level did:there was no significant difference between degreeⅠ and Ⅱ,and Ⅰ did better on FCR than Ⅲ significantly(P<0.05).As the protein level and satiation degree increased,NH⁺₄-N,NO^-₂-N excretion and total baneful nitrogen excretion were enhanced(P<0.01).The total baneful nitrogen excretion in group C was 54.5% and 64.4% lower than group D and E respectively,that in degree Ⅰ was 17.8% and 29.2% higher than Ⅱand Ⅲ ,respectively;(2)The activity of protease enhanced,lipase reduced and amylase increased at first,then reduced with increased protein level.As satiation degree increased,digestive enzyme reduced.digestive enzyme of liver was higher than intestine;(3)The relationship between nitrogen excretion and the weight gain as the increasing dietary protein levels,partially accorded with the Rhomb character.By regression analysis,the optimum eco-nutrition requirement of protein for juvenile C.semilaevis seemed to be 48.30%,49.27% and 50.67%,respectively in degree Ⅰ,Ⅱ and Ⅲ.The optimum eco-aquatic requirement of satiation was 90%.