Effect Of Stocking Density On Lipid Accumulation And The Expression Level Of Genes Related To Lipid Metabolism In Grass Carp Ctenopharyngodon Idella

The phenomenon of excessive accumulation of lipid in fish is more and more popular in the current aquaculture.Excessive accumulation of lipid in fish not only wastes feed resources,but also affects the muscle quality,immunity,stress tolerance and so on.At present,the study of fish fat accumulation has been reported a lot in the field of fish feed and nutrition.However,the current excessive accumulation of lipid in fish is not a simple nutrition or feed problems,but a multi-factor integrated role.The environmental factors affect on fish lipid accumulation and mechanism is also worthy of study.Therefore,this study explored the effect of stocking density on lipid accumulation and the expression level of genes related to lipid metabolism in grass carp.There were three stocking densities,it was 5,15,30 ind / tank(2.4kg/m3?7.4kg/m3?14.9kg/m3),4 repetitions were given in each group,and the feeding period was 70 days.After the experiment,the fish growth indexs were measured,and the blood,muscle,liver and mesenteric adipose tissue of the grass carp were taken to measure the blood biochemical indexes,nutritional indexes,muscle tissue sections and the mRNA expression of lipid metabolism related genes.The results are as follows:1.The culture density had significant effect on the growth performance,blood biochemical indexes and body composition of grass carp(p<0.05).final body,final length,weight gain,specific growth rate,feeding rate,viscera index and mesenteric lipid index decreased significantly with the increasing stocking density(p<0.05).The diameter of the muscle fibers in the dorsal muscles and in the bottom part of the abdominal muscle of the LSD and MSD was significantly higher than that of the HSD(p<0.05).The levels of total triglyceride(TG),total cholesterol(TCHO)and high density lipoprotein content(HDLC)in the serum of high stocking density group were the lowest(p<0.05).With the increasing stocking density,the crude lipid content in the dorsal muscle,the bottom part of abdominal muscle,the liver and the mesenteric adipose tissue was negatively correlated with the culture density,while the result of the water was the opposite(p<0.05).The values of dicosylhexaenoic acid(DHA),arachidonic acid(EPA)and n-6 / n-3 in the muscle of grass carp increased with the increasing stocking density,and the content of most amino acids of grass carp was increased first and then decreased with the increase in the stocking density(p<0.05).2.The contents of lipid droplets and lipoprotein lipase(LPL)activity in the liver of grass carp were the highest in the medium density group and the lowest in the LSD(p<0.05).The expression of growth hormone receptor gene(GHR)in the dorsal muscle,the bottom part of abdominal muscle,liver and mesenteric adipose tissue trended consistent,and they increased significantly with the increase in the stocking density(p<0.05).The expression of cortisol receptor(GR)gene and LPL gene in muscle was consistent.The expression of androgen receptor(AR)gene was significantly different between different culture densities in mesenteric adipose tissue(p<0.05).In the bottom part of abdominal muscle,the expression level of lipidty acid synthase gene(FAS)was the lowest in the LSD(p<0.05);the expression level of LPL gene increased first and then decreased with the increase of stocking density,and was the lowest in the HSD(p<0.05);The significant highest expression of hormone-sensitive lipase(HSL)gene was occurred in HSD(p<0.05);Acetyl-Co A carboxylase(ACC)gene,carnitine palmitate transferase I(CPT-I)gene,Peroxisome proliferator-activated receptor ?(PPAR?)gene and leptin gene in different density groups had no significantly in different stocking density(p<0.05).In the liver tissue,The highest mRNA expression levels of FAS,ACC,LPL,HSL,CPT-I and PPAR? was observed in MSD(p<0.05),and there was no significant difference between the LSD and HSD;The highest mRNA expression levels of leptin was in HSL.In the mesenteric adipose tissue,the mRNA expression levels of FAS,ACC and CPT-I in the high density group were significantly higher than those in LSD and MSD(p<0.05);the expression level of LPL in the high density group was the lowest;the mRNA expression level of leptin was highest in the HSD(p<0.01).The results showed that the high culture density decreased the growth performance of grass carp and caused the massive consumption of energy,which resulted in the significant decrease of TG,TCHO and HDLC content in blood.The crude lipid content of the dorsal muscle,the bottom part of abdominal muscle,liver and mesenteric adipose tissue was significantly reduced.A certain stocking density could promote the accumulation of lipid in the liver.The high culture density may promote the expression of GHR gene.Under certain culture density,the mRNA expression of GR and LPL gene in the bottom part of abdominal muscle of grass carp can be promoted,which indicated that the mechanism of abdominal lipid accumulation in grass carp under chronic congestive stress was complete inconsistent with that of higher animal.The mRNA expression levels of FAS,ACC,LPL,HSL,CPT-I,PPAR? and leptin in the bottom part of abdominal muscle,liver and mesenteric adipose tissue of grass carp were significantly different,but the mRNA expression trend was inconsistent,indicating that the effects of crowding stress on the mRNA expression of fish lipid metabolism related gene had tissue specific in grass carp.Leptin gene could reduce the feeding rate of grass carp.