| Temperature is one of the most important environmental factors in aquaculture,and protein is the most important nutrient element for animal growth.There are some reports on the interaction of temperature and protein on the physiological response of fish,but it is rare in shrimps and crabs.This experiment takes Macrobrachium nipponense as the research object,assesses the optimal protein requirements of Macrobrachium nipponense at different temperatures from the perspectives of growth,and then From the perspective of immunity and antioxidant capacity,explores how temperature stress causes changes in the protein requirements of Macrobrachium nipponense,and finally,from the perspective of protein metabolism,we will discuss how Macrobrachium nipponense regulates protein requirements to meet its growth under temperature stress.The experimental subjects were Macrobrachium nipponense with a body weight of(0.66±0.03g).Three different dietary protein levels(P34,P38 and P42)were fed under different water temperature(T20,T25 and T30).A total of nine groups,and the breeding experiment period was 58 days.The main results of this study are as follows:1.The influence of temperature and protein level on the growth performance and body composition of Macrobrachium nipponenseThe results showed that the interaction of temperature and protein level had a significant effect on the AFW and WGR of Macrobrachium nipponense(p<0.05).The AFW and WGR of the T25/P34,T25/P38,T25/P42 and T30/P34 groups were significantly higher than the other five groups.Water temperature had a significant effect on AFW,SR,WGR,SGR,FCR,RFI and PER(p<0.05).The AFW,WGR and SGR of the T25 group were significantly higher than those of the T20 and T30 groups,while the FCR was lower than the T20 and T30 groups.With the increase of water temperature,RFI increased significantly,while PER and SR decreased significantly.Dietary protein level only had a significant effect on AFW,PER and RFI(p<0.05).The AFW of the P38 group was significantly higher than that of the P42 group and also higher than that of the P34 group,but the effect was not significant.With the increase of protein level,RFI increased significantly,while PER decreased significantly.The interaction of temperature and protein level only had a significant effect on crude fat(p<0.05).The crude fat in the T20/P34 group was significantly higher than the other eight groups.Also,the crude body fat of the shrimp in the T20/P38 group was significantly higher than that in the T20/P42,T25/P38,T25/P42,T30/P38 and T30/P42 groups.The water temperature had a significant effect on the crude protein and crude fat of the shrimp body(p<0.05).The crude protein content of the T20 group was significantly lower than that of the T25 and T30 groups,while the crude fat content was significantly higher than that of the T25 and T30 groups.The dietary protein level only had a significant impact on the crude fat content(p<0.05).As the protein level increased,the crude fat content significantly decreased.The results showed that according to WGR,25℃ is the suitable water temperature for the growth of Macrobrachium nipponense.At 20°C,25°C and 30°C,the optimal protein requirements of Macrobrachium nipponense were 38%,42% and 34%,respectively.This indicated that too high and too low temperature stress will reduce the protein demand of Macrobrachium nipponense.2.The effect of temperature and protein level on the antioxidant and immune performance of Macrobrachium nipponenseThe results showed that the interaction of temperature and protein level has a significant effect on hemolymph SOD,CAT,MDA,NO and i NOS(p<0.05).Also,water temperature had a significant effect on hemolymph SOD,CAT,NO and i NOS(p<0.05).The levels of SOD,CAT,NO and i NOS in the T25 group were significantly higher than those in the T20 and T30 groups.The dietary protein levels had a significant effect on SOD and MDA(p<0.05).In the T20 group,the levels of NO and i NOS in the P38 group were higher than those in the P34 and P42 groups,while the MDA level was lower than that in the P34 and P42 groups.SOD levels increased significantly with the increase of protein levels.In the T25 group,the levels of SOD,CAT,NO and i NOS increased with the increase of protein levels,while the MDA level decreased significantly.In the T30 group,the levels of SOD,CAT,NO and i NOS in the P34 group were higher,and the MDA level was lower.Besides,the interaction of temperature and protein level had a significant impact on the expression of Toll,Dorsal,Myd88,IMD,Relish,HSP60 and HSP70(p<0.05).Also,temperature also had a significant effect on the expression of these genes(p<0.05).With the P38 and P42 groups.Compared with P38/T30 and P42/T30,P34/T30 had lower levels of AST,ALT,SDH and XOD.Also,the interaction of temperature and protein level had a significant effect on hepatopancreas TOR,S6K2 and 4E-BP1(p<0.05).Also,temperature had a significant effect on the expression of these genes(p<0.05).The expression of TOR,S6K2 and 4E-BP1 in the T25 group were significantly higher than that in the T20 and T30 groups,while the expression of 4E-BP1 was significantly lower than that in the T20 and T30 groups.The dietary protein level had no significant effect on the expression of these genes(p>0.05).In the T20 group,the expression levels of TOR and S6K2 in the P38 group were higher than those in the P34 and P42 groups,while the expression of 4E-BP1 was significantly lower than that in the P34 and P42 groups.In the T25 group,the expression levels of TOR and S6K2 in the P42 group were higher than those in the P34 and P38 groups,while the expression of 4E-BP1 was lower than the other two groups.In the T30 group,as the protein level increased,the expression levels of TOR and S6K2 gradually decreased,and the expression level of 4E-BP1 also increased.The results of TOR,S6K2 and 4E-BP1 in muscle were similar to those in hepatopancreas.The results showed that when subjected to temperature stress,high-protein diet can inhibit the m TOR signaling pathway,thereby reducing protein synthesis and inhibiting growth.In summary,this study shows that low temperature or high temperature stress will reduce the protein requirements of Macrobrachium nipponense,leading to a decline in the body’s immune and anti-oxidant abilities,easily causing oxidative stress damage,inhibiting the m TOR signaling pathway,reducing protein synthesis,and inhibiting the growth of shrimp.Compared with high protein,reducing protein levels is more conducive to alleviating oxidative damage.At 20°C,25°C and 30°C,the optimal protein requirements of Macrobrachium nipponense are 38%,42% and 34%,respectively. |
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