| The present study investigated the effects of different carbohydrate-to-lipid(CHO:LIP)ratios on the growth performance,carbohydrate and lipid metabolism,and innate immunity of red swamp crayfish(Procambarus clarkii),and determined the optimal CHO: LIP ratio requirements of red swamp crayfish in diets.The findings enriched the system of basic research on the nutritional metabolism of crustaceans and provided a scientific basis for the development of high-energy,low-protein diets for red swamp crayfish and the protein-sparing effect in aquafeeds.This study contains the following three main components:1.Effects of different CHO: LIP ratios of diets on growth performance,antioxidant capacity,and abdominal muscles proximate composition of red swamp crayfishFour isonitrogenous and isoenergetic experimental diets were prepared with fishmeal,soybean meal,and rapeseed meal as protein sources,soybean oil as lipid source,and corn starch as carbohydrate source.A total of 420 red swamp crayfish(initial weight 9.10 ± 0.15)g were selected and randomly divided into 4 groups of 3replicates each with 35 red swamp crayfish in each replicate.The groups were fed the four experimental diets separately and the culture period was 8 weeks.The results showed that(1)The group with a CHO: LIP ratio of 5.94 had the highest growth performance and the lowest feed conversion rate(FCR),which was significantly different from the CHO: LIP ratio of 1.88,3.25,and 13.60(P < 0.05).There were no significant effects of diet CHO: LIP ratio on survival rate(SR)and hepatopancreas somatic indices(HSI)of red swamp crayfish(P > 0.05).(2)Total antioxidant capacity(T-AOC),catalase(CAT),and superoxide dismutase(SOD)activities in the hemolymph and hepatopancreas of red swamp crayfish had maximum values in the group with a CHO: LIP ratio of 5.94,significantly higher than those in the groups with a CHO: LIP ratio of 1.88,3.25 and 13.60(P < 0.05),and malondialdehyde(MDA)content in the hemolymph and hepatopancreas showed an opposite trend,with minimum values in the group with a CHO: LIP ratio of 5.94(P < 0.05).(3)Red swamp crayfish abdominal muscle crude lipid content had the lowest value in the 13.60 group and was significantly lower than that in the 1.88,3.25,and 5.94 groups(P < 0.05).The crude protein content of the abdominal muscles of red swamp crayfish had a maximum value in the group with a CHO: LIP ratio of 5.94,which was significantly higher than that of the groups with a CHO: LIP ratio of 1.88 and 3.25(P < 0.05).There were no significant effects of diet CHO: LIP ratio on the crude ash and moisture contents of the abdominal muscles of red swamp crayfish(P > 0.05).The results showed that an optimal CHO: LIP ratio(5.94)enhanced the antioxidant capacity,and is more beneficial to the growth performance of red swamp crayfish.2.Effects of different CHO: LIP ratios of diets on the digestive and absorptive capacity,hemolymph biochemical indexes,carbohydrate and lipid metabolism of red swamp crayfishThe experimental design and feeding scheme were the same as in Experiment 1.The results showed that:(1)The intestinal amylase and protease activities of red swamp crayfish had a maximum value in the group with a CHO: LIP ratio of 5.94,which was significantly higher than those in the groups with a CHO: LIP ratio of 1.88,3.25 and13.60(P < 0.05).Intestinal lipase activity decreased significantly(P < 0.05)with the increase of CHO: LIP ratio from 1.88 to 13.60.(2)The group with a CHO: LIP ratio of13.60 had the lowest hemolymph cholesterol level,which was significantly lower than all other groups(P < 0.05).However,the opposite trend was observed in hemolymph glucose levels(P < 0.05).There was no significant effect of dietary CHO: LIP ratio on the hemolymph triglyceride levels of red swamp crayfish(P > 0.05).(3)Hepatopancreatic phosphofructokinase(PFK)activity and m RNA expression levels of pfk,pyruvate kinase(pk),lactate dehydrogenase(ldh),fatty acid synthase(fas),cholesterol regulatory element binding protein 1(srebp1),retinoic acid X receptor(rxr)and hexokinase(hk)genes had the maximum value in the group with a CHO: LIP ratio of 13.60,which was significantly higher than the groups with a CHO: LIP ratio of 1.88,3.25 and 5.94(P < 0.05).However,the activities of lipoprotein lipase(LPL),hepatic esterase(HL),and phosphoenolpyruvate carboxykinase(PEPCK),the m RNA expression levels of acyl coenzyme a oxidase(aco),fatty acid binding protein(fabp),acyl coenzyme A synthase(acsbg),glucose 6-phosphatase(g6pase),pepck and fructose-1,6-bisphosphatase(fbpase)genes had minimum values in the 13.60 CHO:LIP ratio group and were significantly lower than those in the 1.88,3.25 and 5.94 CHO:LIP ratio groups(P < 0.05).The results of the study indicated that the appropriate CHO:LIP ratio(5.94)in the diet could facilitate the absorption and utilization of nutrients by red swamp crayfish.At the same time,red swamp crayfish can respond to the changes of carbohydrate and lipid levels in the diet by regulating substance metabolism processes(gluconeogenesis,glycolysis,lipid generation,and lipid degradation).3.Effects of different CHO: LIP ratios of diets on innate immunity and TLRMAPK/NF-κB signaling pathway in red swamp crayfishThe experimental design and feeding scheme were the same as in Experiment 1.The results showed that(1)alanine aminotransferase(ALT),aspartate aminotransferase(AST),acid phosphatase(ACP),alkaline phosphatase(AKP)activities and albumin(ALB)levels in the hemolymph of red swamp crayfish had the lowest values in the group with a CHO: LIP ratio of 5.94 and were significantly lower than those in the groups with a CHO: LIP ratio of 1.88,3.25 and 13.60(P < 0.05).However,hemolymph lysozyme(LZM)activity,total protein(TP),and globulin(GLB)contents showed the opposite trend,with maximum values in the group with a CHO: LIP ratio of 5.94,significantly higher than those in the groups with a CHO: LIP ratio of 1.88,3.25 and13.60(P < 0.05).(2)The hepatopancreas and intestines in CHO: LIP ratio of 3.25 and5.94 groups had the best histological morphology,with tightly arranged hepatopancreas epithelial cells,smaller vacuoles,uniform size,and larger B cells present.In the intestinal sections,normal nuclei and well-arranged,morphologically normal epithelial cells were observed,with no obvious vacuoles.(3)The expression levels of TLRMAPK/NF-κB signaling pathway-related genes(tlr3,myd88,and mapk3)in the hepatopancreas had the lowest values in the CHO: LIP ratio of 5.94 group and were significantly lower than those in the CHO: LIP ratio of 1.88,3.25 and 13.60 groups(P< 0.05).The expression levels of hepatopancreas nf-kb α,nf-kb β,nf-kb p105,and traf6 genes were significantly higher in the CHO: LIP ratio 5.94 group than in the CHO: LIP ratio 1.88,3.25 and 13.60 groups(P < 0.05).The differences in the expression levels of mapk7 and p38 mapk genes between the groups did not reach significant levels(P >0.05).(3)The expression of immune-related genes including hsp70,gpx,cat,mnsod,cuznsod,gst and cypa had the maximum values in the group with a CHO: LIP ratio of5.94,which was significantly higher than that in the groups with a CHO: LIP ratio of1.88,3.25 and 13.60(P < 0.05).There were no significant differences in CHO: LIP ratio on the change of crustin gene expression levels(P > 0.05).The results of the study showed that red swamp crayfish had strong innate immunity under the appropriate CHO:LIP ratio(5.94).In addition,the damage to tissues and organs was minimal at this CHO:LIP ratio.Unsuitable CHO: LIP ratios(1.88,3.25,and 13.60)inhibited the innate immunity of red swamp crayfish and activated inflammation-related signaling pathways.Based on the above findings,it is clear that an appropriate CHO: LIP ratio(5.94)plays an important role in promoting growth,enhancing antioxidant capacity and innate immunity,and suppressing the expression of genes in inflammation-related signaling pathways to maintain the health of the intestinal and hepatopancreas of red swamp crayfish.In conclusion,a dietary CHO: LIP ratio of 5.94(approximately 36.23%carbohydrate and 6.10% lipid)was found to be optimal for the physiological condition and health status of red swamp crayfish. |
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