池塘低碳培育条件下长吻鮠当年鱼种的生长特性及消化、抗氧化、非特异性免疫、代谢相关酶活性研究OA

To explore the changes in growth characteristics,digestive capacity,antioxidant capacity,non-specific immunity and metabolic capacity of current-year juveniles of Leiocassis longirostris under low-carbon pond culture conditions,this study took the same batch of artificially bred current-year juvenile L.longirostris as research objects,and carried out a 112-day aquaculture experiment by adopting natural live biological baits self-cultivated in the pond without feeding artificial compound feed.The results showed that the experimental group juveniles grew rapidly during the early-mid stage(first 84 days),with body mass gain faster than body length gain,showing the characteristics of rapid growth.The length(L)-weight(W)relationship followed a power function:W=O.029 L2 7144(R2=0.960 8,P＜0.01).After entering the late culture stage(84 days later),the increasing rate of specific growth rate of the experimental juveniles slowed down,and growth stagnation occurred.In terms of digestive enzymes,the amylase activities in intestinal and gastric tissues of juvenile L.longirostris in the experimental group showed a declining trend with the prolongation of culture time.The protease activity in gastric tissues was relatively stable,while the protease activity in intestinal tissues presented a trend of firstly decreasing,then leveling off,and finally rising.The amylase and protease activities in the intestine were significantly higher than in the stomach(P＜0.05).In terms of antioxidant enzymes,the hepatic superoxide dismutase(SOD)activity of juvenile L.longirostris in the experimental group fluctuated in a wavy pattern during the early and middle culture stage(the first 84 days)and increased gradually in the late culture stage(after 84 days),while the activities of catalase(CAT)and glutathione peroxidase(GSH-Px)remained stable throughout the culture period.Regarding non-specific immunity enzymes and metabolic enzymes,the alkaline phosphatase(AKP)activity of juvenile L.longirostris in the experimental group showed a wavy downward trend with the extension of culture time.The acid phosphatase(ACP)activity fluctuated in a wavy pattern during the early and middle culture stage(the first 84 days)and declined gradually in the late culture stage(after 84 days);moreover,ACP activity was obviously higher than AKP activity throughout the whole culture period.Alanine aminotransferase(ALT)activity had no significant change with the prolongation of culture time,whereas aspartate aminotransferase(AST)activity fluctuated with a trend of decreasing,increasing,decreasing and rising successively during the early and middle culture stage(the first 84 days),and then decreased gradually in the late culture stage(after 84 days).In conclusion,under low-carbon pond culture,the growth inflection point of juvenile L.longirostris in the experimental group occurred on day 84.They grew rapidly within the first 84 culture days and could be cultured relying on natural live biological baits alone;after 84 days of culture,natural live biological baits alone could hardly satisfy their growth and physiological demands.Based on the growth and physiological changes of the experimental juveniles,to sustain their healthy growth,special compound feed with high crude protein and high fatty acid shall be supplementally fed starting from the 84th culture day.The recommended indicators are crude protein content＞38％and crude lipid content＞10％(both are mass fractions).