The Study On Lipid Nutrition Of Juvenile And Post-larval Redclaw Crayfish, Cherax Quadricarinatus

Red claw crayfish (Cherax quadricarinatus) which was also called Australian freshwater crayfish was fisrt introduced to Guangzhou, China in 1992. It subordinated to Crustacea, Decapoda, Pleocyemata, Astacidea, Parastacoidea, Parastacidae, Cherax. Recent years, as the cultivation scale increased, it is urgent for us to know the nutrients need of crayfish, but little studies were focused on it. More studies were focused on the protein, carbon componds and vitamins needed for juvenile crayfish, or lecithoid, cholesterol and long-chain PUFA needed for adult crayfish. Choosing the right lipid sources for culturing can not only sufficiently enhance the growth and food utilization rate, but also reduce the cost and improve the surival rate of juvenile individuals. Based on the formal studies, in order to know the lipid need of juvenile crayfish, this study was conducted to evaluate the effects of dietary lipid sources (peanut oil, pork lard, fish oil and soybean oil) on growth, digestive enzyme activity, fatty acid composition and ultrastructure of hepatopancreas in post-larval and juvenile red claw crayfish using the methods of electron microscope, histology and enzymology. The data obtained would provide valuable information to the development of artificial diets for Cherax quadricarinatus.Using the biological measuring methods, we compared the length growth rate, special growth rate, weight gain, hepatopancreatic index and survival rate of red claw crayfish fed by different lipid sources. There was no significant effects (P> 0.05) on length growth rate and special growth rate among all treatments. However, the treatment with soybean oil had significantly (P< 0.05) higher weight gain (2332.93%) and hepatopancreatic index (0.75%) than other groups. But the lowest weight gain (1839.50%) was found in peanut oil group. Different lipid sources had different effects on growth indexs of red claw crayfish. Totally, the crayfish can better utilized the food with soybean oil, although fish oil was abundant in DHA and EPA. We used the biochemical methods to measure the effects of different lipid sources on digestive enzyme activity (pepsin, lipase, amylase and cellulase) in hepatopancreas of post-larval and juvenile red claw crayfish. They showed different digestive enzyme activity to different lipid sources. The result reflected that post-larval and juvenile red claw crayfish had a different adaptation to different diets.Analysis of digestive enzyme profiles from the hepatopancreas revealed a positive correlation between lipase, amylase, cellulase activities and the diet lipid sources, although there was no significantly different (P> 0.05) in pepsin activity. The treatment with fish oil had the highest lipase activity, and together with soybean oil, the lipase activity is 2-3 times higher than that of peanut oil and pork lard groups, but still lower than commercial group. Amylase activity was highest in pork lard group, but lowest in fish oil treatment. Crayfish larva showed low cellulase activity in any group, soybean oil and pork lard groups had higher activity (0.11μg/min) than other lipid sources. The results suggested that the post-larval red claw crayfish needed more protein and lipid than carbohydrate. So, we should add more protein to their food in the early days of culturing.Different lipid sources had no significant effects on pepsin activity of juvenile crayfish. Peanut oil group had the highest lipase activity (1177.23U/gprot). Amylase activity was significantly (P< 0.05) different in different diets, and fish oil group has the highest activity. Cellulase activity is higher in peanut oil group (61.14μg/min) than other groups. The result implied that vegetable oil had a role in promoting fat metabolism to juvenile red claw crayfish, and the soybean oil is better than peanut oil. So, maybe we could add more starch ingredients to the diet of juvenile crayfish, which can improve diet's utilization and reduce the cost. However, the effective utilization of the carbohydrate needs further study.The same lipid source had a different effect on post-larval and juvenile red claw crayfish. Post-larval crayfish had a higher pepsin activity than juvenile crayfish, but amylase and cellulase activity were significantly lower in post-larval crayfish. Through the change of activity of digestive enzyme, we can see that feeding habits is partial animal feeding in post-larval crayfish but partial plant feeding with the growth of individual. So, larva should be fed diets containing suitable ingredients at different stages of individual to improve utilization of diets.We researched the effect of different lipid sources on fatty acid composition of hepatopancreas and tail muscle in post-larval and juvenile red claw crayfish using biochemistry methods. Fatty acids composition including Saturated fatty acids (SFA), Mono-unsaturated fatty acids (MUFA) and Poly-unsaturated fatty acids (PUFA) of in tail muscle and hepatopancreas were affected by different lipid sources. Meanwhile, we compared the ultra structure of hepatopancreas in post-larval crayfish fed different diets.Fed different lipid sources,16-22 fatty acids were detected in tail muscle and hepatopancreas. Polyunsaturated fatty acids is mainly based on linoleic acid (C18: 2n6) in hepatopancreas, but linoleic acid (C18:2n6) and EPA (C20:5n3) in tail muscle. The result reflected composition and using feature in post-larval crayfish growth. Content of polyunsaturated fatty acids in tail muscle were higher than hepatopancreas, which suggested that fatty acids, especially linoleic acid (C18:2n6), linolenic acid (C18:3n3) and EPA (C20:5n3), were transported to muscles first to supply energy metabolism require for growth. Soybean oil can promote not only fatty acids metabolism but also digestive enzyme activities, because of rich in linoleic acid (C18: 2n6) and good value of fatty acids.The ultra structures of hepatopancreas in post-larval crayfish were studied with electron microscopes. Cell type in hepatopancreas epithelium was same fed different diets, classified into E-cell, B-cell, R-cell and F-cell based on structure and function. But ultra structure of R-cell (Resorptive cell) was affected significantly in different treatment. Defect of membrane in R-cell of pork lard group suggested that as lipid source, pork lard couldn't meet growing nutritional needs of post-larval red claw crayfish. Pork lard might lead to metabolic disturbances, and thereby affecting the survival rate. Rich store of lipid droplets in R-cell of soybean oil group was the reason for high survival rate.The content of fatty acids in tail muscle and hepatopancreas was obviously affected by the variety and content of fatty acids in dietary. Saturated fatty acid content in hepatopancreas to lard group was significantly higher than other groups, which is similar in the tail muscle. Monounsaturated fatty acid had the highest content to peanut oil group, and lowest to soybean oil group, but its content was higher in two animal oil groups than two plant oil groups. The content of linoleic acid (C18:2n6) and linolenic acid (C18:3n3) were highest in soybean oil group than all other four groups in tail muscle, which was consistent with hepatopancreas. Accumulation of linoleic acid showed needs and utilization feature of juvenile crayfish. The result suggested adding moderate soybean oil as lipid source could promote the accumulation of essential fatty acids, and improve growth and survival rate.