| The first experiment was conducted to investigate the effects of feed fat,carbohydrates,and their interactions on growth performance,feed utilization,body composition,and nonspecific immunity of pearl gentian grouper(Epinephelus lanceolatus?×E.fuscoguttatus?).In a 3x3 factorial design,9 isogenic nitrogen feeds were formulated with 3 fat levels(7%,10%,and 13%)and carbohydrate levels(8%,12% and 16%).In one treatment group,30 juveniles(initial body weight,21.48±0.24 g)were fed in parallel and fed twice a day for 8 weeks.The results showed that the specific growth rate(SGR)of grouper was not affected by feed fat content(P > 0.05),but it decreased significantly with increasing feed carbohydrate content(P < 0.05).Among them,groupers fed with 10% fat and 8% sugar feeds obtained the highest SGR.High dietary fat or carbohydrate significantly reduced food intake(FR)(P < 0.05)but significantly improved feed efficiency(FER)and protein efficiency(PER)(P < 0.05).In addition,protein retention rate(PRR)and fat retention rate(LRR)increased significantly with increasing feed fat levels(P < 0.05),while LRR decreased significantly with increasing feed carbohydrate content(P < 0.05).The interaction between feed sugars and fats significantly affected the use of feed(P < 0.05).With the increase of feed fat or carbohydrate content,the apparent digestibility of starch(ADC)decreased significantly(P < 0.05),and the interaction effect was also significant(P < 0.05).The protein content of liver,muscle and whole fish of grouper significantly decreased(P < 0.05),and the fat content increased significantly with the increase of feed fat content(P < 0.05).In addition,an increase in feed carbohydrates resulted in a significant decrease in liver crude protein and fat(P < 0.05),but a significant increase in hepatic glycogen content(P < 0.05).The groupers were fed diets containing 8%,12%,and 16% of sugar,and the postprandial blood glucose levels peaked at the time points of 3,6,and 12 hours,respectively.With the increase of feed fat content,serum lysozyme activity increased significantly(P < 0.05).With the increase of sugar content in feed,serum lysozyme activity decreased significantly(P < 0.05),and its interaction The effect was not significant(P > 0.05).In addition,the highest SOD activity was obtained in the grouper fed with 10% fat diet,but it had no significant effect on the increase of feed carbohydrate content(P > 0.05).These results indicate that 10-13% fat and 8% carbohydrates should be optimal in this grouper's feed combination.The second experiment aimed to continue to investigate the effects of digestible starch in feed on the growth,feed utilization,body composition and nonspecific immunity of pearl gentian grouper(Epinephelus lanceolatus?×E.fuscoguttatus?).By adding starch,7 types of feeds,including 2.67%,6.19%,9.06%,12.56%,15.66%,18.97%,and 21.39% of egg and other fats(48.51%,11.84%),were obtained.Thirty-five test fish with an initial body weight of(9.16±0.04)g were stocked in each bucket.Each treatment group consisted of three replicates.Each day,they were fed two times(8:00 and 16:00),and normal light was used for breeding.week.The experimental results show that the digestible starch in the feed did not affect the survival rate of the experimental fish.When dietary digestible starch exceeded 6.19%,the final body weight,specific growth rate and feeding rate of experimental fish decreased significantly(P < 0.05).When the digestible starch was 9.06%,the feed efficiency reached the highest(P < 0.05).With the increase of digestible starch,the digestibility of protein,fat and starch in feed decreased significantly(P < 0.05),but the difference in protein digestibility was not significant(P > 0.05)when the starch level was below 12.56%;The protein content of whole fish,muscle and liver decreased significantly with the increase of starch in the feed(P < 0.05),and the crude fat content increased first and then decreased with the increase of starch in the feed(P > 0.05);Liver glycogen and muscle glycogen content increased significantly with the increase of the starch level in the feed(P < 0.05);the experimental fish liver to body ratio increased with the level of starch in the feed.Significantly increased(P < 0.05);the ratio of body weight to experimental fish increased as the level of starch in the diet increased,and there was no significant difference in the D6.19-D21.39 group.The activity of SOD in the viscera of experimental fish was significantly increased with the increase of starch in feed(P < 0.05).When the digestible starch was 6.19%,serum lysozyme activity and protein content were the highest(P < 0.05).After 9.06%,serum lysozyme activity decreased significantly(P < 0.05).Using the specific growth rate and feed efficiency as indicators,the appropriate levels of digestible starch in feed were 6.19% and 9.06%,respectively.This study shows that the ability of pearl gentian grouper to digest starch in feeds is limited.The third experiment was conducted to investigate the effects of insulin on plasma glucose,hepatic glycogen content and expression of glucose metabolism related genes in hybrid grouper.Triplicate groups of five fish were sampled at 0,1,3,6,12,24 h or 48 h post bovine insulin(5?g per 100 g fish body mass).Significant decrease of plasma glucose was observed along with the depletion of hepatic glycogen content at 12 h after insulin injection.The results of hepatic gene expression analysis revealed that the infusion of insulin significantly increased the expression of glucose transporters,GLUT1 and GLUT2.The transcription of gluconeogenesis related genes,fructose-1,6-bisphosphatase 1(FBPase 1)and glucose-6-phosphatase catalytic subunit(G6PC),were significantly decreased at 12 h post insulin infusion,while the expression of glycolysis related genes,6-phosphofructokinase liver type(PFKL)and pyruvate kinase liver type(PKL),were significantly up-regulated at 24 h post injection.Notably,the elevation of glucokinase(GK)expression following insulin administration was remarkably higher than other genes.As for glycogen metabolism process,the expression of glycogen synthase liver type(GYS2)was significantly decreased at 12 h post insulin injection,while the expression of glycogen phosphorylase liver type(PYGL)was significantly elevated at 24 h time-point.These results suggested that insulin could affected glucose metabolism through regulating gluconeogenesis,glycolysis and glycogen metabolism at the transcription level.The ability to utilize the digestible starch in the feed is limited.The overdigestible starch in the feed will affect the growth,and also cause the high carbohydrate level after meal.The suitable carbohydrate level in the feed should be no more than 8%.The appropriate level of fat in the feed should be 10 to 13%,and the content of suitable digestible starch in feed(crude protein 48.51%,crude lipid 11.84%)should be between 6.19 to 9.06%.Better growth and feed efficiency at this level.Insulin can affect glucose metabolism by modulating transcriptional levels of gluconeogenesis,glycolysis,and glycogen metabolism. |
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