Studies About The Utilization Of Dietary Carbohydrate Of Mud Crab Scylla Paramamosain

The mud crab Scylla paramamosain is an important marine crab species in China,but the nutrition research of it is still scarce,which is the main factor to restrict the large-scale culture of S.paramamosain.As one of the three major nutrients,carbohydrate is the cheapest energy source in diet,which can spare protein and reduce diets costs.The natural diets of mud crabs contain a certain amount of carbohydrates,which indicates that the mud crab could utilise carbohydrates.In order to evaluate dietary carbohydrate sources and levels on the growth and physiological metabolism of S.paramamosain,to understand the ability of carbohydrate in mud crab.Two experiments were designed in this paper.The results and conclusions are as follows:1.Dietary carbohydrate sources on growth,feed utilization,body composition and glycogen content of Scylla paramamosainSix different carbohydrate sources were designed in the experiment,namely glucose,sucrose,dextrin,wheat starch,corn starch,and cassava starch,with the level of 20%.Fish meal and casein were used as protein sources at 45%,fish oil and soybean oil were used as lipid sources at 9.5%,and use cellulose to adjust the equal energy among the groups.The initial weight of mud crab is 0.71±0.03 g.The treatment lasts 8 weeks.During the experiment,the daily mortality and molting were recorded.The results showed that the final body weight,weight gain rate,body composition and glycogen content of mud crab of S.paramamosain were significantly affected by diet carbohydrate sources(P<0.05).The result of survival rate: corn starch>cassava starch>dextrin>wheat starch>glucose>sucrose.Weight gain rate: cassava starch>corn starch>dextrin>wheat starch>sucrose>glucose.Different carbohydrate sources have notable effects on the feed utilization of S.paramamosain.The feed conversion rate of the glucose group is the highest,which is significantly higher than the corn starch group,the cassava starch group and the dextrin group(P<0.05).The corn starch group was the highest in protein efficiency ratio,which issignificantly higher than the glucose group.The molt frequency(MF)of the juvenile mud crabs in the sucrose group and the cassava starch group was higher than the glucose group,and there was no statistical difference with other groups(P>0.05).Different treatments had no significant effects on moisture,body protein and ash,but had significant effect on body lipid content in mud crab(P<0.05).The body lipid content of the cassava starch group is higher than the glucose group.In addition,the sucrose group and the corn starch group have higher hepatic glycogen content than other groups.In summary,the results showed that the corn starch was the suitable carbohydrate sources for the growth performance of mud crab S.paramamosain.2.Effects of dietary carbohydrate levels on growth,body composition,and gene expression of key enzymes involved in hepatopancreas metabolism in mud crab Scylla paramamosainWe used gelatinized corn starch as the only carbohydrate source,and five different carbohydrate levels were set at 8.55%,13.36%,17.76%,25.64% and32.50%,respectively.Same as test 1,the level of protein was 45% and the level of lipid was 9.5% to meet the nutritional requirements of mud crab.The initial weight of mud crab is 1.84±0.07 g,and the treatment lasts 8 weeks.Indoor culture conditions are similar to test 1.The results showed that different carbohydrate levels had significant effects on the growth of S.paramamosain.After the polyline regression analysis,the mud crab of S.paramamosain obtained the maximum weight gain rate at24.08% dietary carbohydrate level.The body lipid content,hemolymph glucose concentrations and hepatic glycogen content of mud crab are significantly affected by the carbohydrate level.Carbohydrate-rich diet led to higher hemolymph glucose concentration and more lipid deposition in the body.Futhermore,through real-time quantitative PCR analysis,the gene expression of glucokinase and fructose2,6-diphosphatase was also affected by carbohydrate level.The mRNA expression of glucokinase was the lowest in 32.50% carbohydrate level,and the gene expression of fructose 2,6-diphosphatase was the highest in 25.64% carbohydrate level.Besides,glucose metabolism will influence lipid metabolism.The gene expression of fatty acid synthase in 25.64% and 32.50% carbohydrate level is 5-fold and 10-fold higher than8.55%,respectively.In the present study,S.paramamosain has a certain tolerance to carbohydrate-rich diet,but too much carbohydrate will result in lipid accumulation in the body,and a 24.08% diet carbohydrate level can gain maximum growth of mud crab.