Effects Of Corn Meal And Soybean Meal In Diets On Digestive Physiology And Immunity Of Sea Cucumber Apostichopus Japonicus

Sea cucumber Apostichopus japonicus has been widely cultured in north of China as an important species for mariculture due to its high nutritional and economic value in recent years. The seaweed Sargassum thunbergii is extensively used as the main ingredient of formulated diet for sea cucumber. However, the low natural productivity and increasing market demand of the S. thunbergii in the formulated diet of sea cucumber is now making the price of S. thunbergii higher and higher. It’s necessary to search alternative ingredients with stable supply and lower price to replace S. thunbergii for sea cucumber farming. The present study aimed to evaluate the feasibility of replacing S. thunbergii with terrestrial plants (corn meal and soybean meal) in the formulated feed of A. japonicas and improve the feed utilization efficiency and immunity of A. japonicas through supplement of exogenous enzymes, glutamine (Gin) and n-3 highly unsaturated fatty acids (HUFAs) in diets. The main results are as follow:1.Effects of replacment of Sargassum thunbergii by the mixture of corn meal and soybean meal on growth,digestive physiology, feed utilization efficiency and fatty acid profiles.4 experimental diets in which S. thunbergii were 0%(contral),20%,40% and 60% replaced with the mixture of corn meal and soybean meal were prepared. The growth rate, body composition and intestinal digestive enzyme activities of A. japonicus fed these 4 diets were examined. Feed utilization efficiency of A. japonicus was determined by means of stable isotope analysis which has been widely used as an effective tool to determine nutrients incorporation from different experimental diets or ingredients. The results show that replacement of S. thunbergii by the mixture of corn meal and extruded soybean meal in formulated diets with suitable proportion (20%) might promote the growth of sea cucumber owing to the relatively higher utilization efficiency of corn meal and extruded soybean meal compared to S. thunbergii. However, further replacement (over 40%) of S. thunbergii by the mixture of corn meal and extruded meal in diets resulted in the decreased utilization efficiency of corn meal and extruded soybean meal by sea cucumber and the subsequent reduction in the growth performance of sea cucumber. Fatty acid compositions of sea cucumber were remarkably affected by the corn meal and soybean meal in diets. Concentrations of fatty acids 16:0,18:2n-6,22:6n-3 and ∑n-6 in sea cucumber appeared to positively correlate with those in the diets. In contrast, contents of fatty acids 20:1n-9,22:1n-9, 20:3n-3,20:4n-6 and 20:5n-3 in sea cucumber showed significant increase with the increasing levels of com meal and soybean meal in diets, even though the contents of these fatty acids in corn meal and soybean meal were lower, even absent, compared with S. thunbergii suggesting that sea cucumber might have the ability to synthesize these fatty acids. Therefore, the optimal replacement proportion of S. thunbergii by the mixture of corn meal and soybean meal ranged between 20% and 40% as A. japonicus.2. Effect of exogenous enzymes supplementation in diets on growth, feed utilization, digestive physiology and immunity of sea cucumber Apostichopus japonicus (Selenka)Five experimental diets were prepared using S. thunbergii, soybean meal and fish meal as the main protein source and containing graded levels of exogenous enzymes (0,0.75,1.5,2.25 and 3 g.kg-1 diet). The exogenous enzymes was consist of cellulose, pectinase, xylanase, glucanase, amylase. The growth rate, ingestion rate, apparent digestibility coefficient and activities of digestive enzymes of A. japonicus fed the 5 experimental diets were determined. It showed that the specific growth rate and apparent digestibility coefficient of A. japonicus were significantly improved when the supplement levels of exogenous enzymes in diets were between.0.75-2.25 g.kg-1 compared to the control group (P< 0.05). And the ingestion rate of A. japonicus in all the treatment groups significantly increased compared to the control group (P< 0.05). However, the activities of trypsin and amylase in the intestine of sea cucumber significantly decreased in the groups in which the levels of exogenous enzymes in diets were over 2.25g.kg-’compared to those in the control group (P< 0.05). And the lipase activity in the intestine of sea cucumber of all the treatment groups significantly decreased cpmpared to that control group (P< 0.05), indicating the supplement of exogenous enzymes in diets inhibited the secretion of digestive enzymes of A. japonicus. The activities of superoxide dismutase (SOD) of sea cucumber significantly increased in the groups in which the levels of exogenous enzymes in diets were over 1.5 g.kg-1 compared to those in the control group (P< 0.05). And the catalase (CAT) activity of sea cucumber of all the treatment groups significantly increased cpmpared to that control group (P< 0.05), indicating the supplement of exogenous enzymes in diets improved the antioxidant capacity of sea cucumber, and immunity of sea cucumber. Thus, the suitable supplementation levels of exogenous enzymes were 0.75-1.5g.kg-1 under this experimental conditions.3. Effects of dietary glutamine (Gin) on growth, digestive physiology,activity and gene expression of immune enzymes of sea cucumber Apostichopus japonicus (Selenka)Five experimental diets were prepared using S. thunbergii, soybean meal and fish meal as the main protein source and containing graded levels of Gln (0%,0.4%, 0.8%,1.2% and 1.6%), and the 0% group was the control group. The specific growth rate, activities of digestive enzymes, activity and gene expression of immune enzymes of A. japonicus fed the 5 experimental diets were determined. It showed that the specific growth rate of A. japonicus significantly improved when the supplement levels of Gln in diets were between 0.4%-1.2% compared to the control group (P< 0.05). The the activities of trypsin in the intestine of sea cucumber significantly increased in 0.8% and 1.6% groups compared to the control group (P<0.05), and the activities of amylase in the intestine of sea cucumber significantly increased in 0.8%, 1.2% and 1.6% groups compared to the control group (P<0.05), and the lipase activity in the intestine of sea cucumber significantly increased in 0.4%,1.2% and 1.6% groups compared to control group (P<0.05), indicating the supplement of Gin in diets improved the secretion of digestive enzymes of A. japonicus. The activities of superoxide dismutase (SOD) of sea cucumber significantly increased in the groups in which the levels of Gin in diets were over 0.4% compared to the control group (P< 0.05), and the catalase (CAT) activity of sea cucumber significantly increased in the treatment groups in which the levels of Gin in diets were over 0.8% compared to that control group (P<0.05). The supplement of Gin in diets exceed 0.4% can up-regulate the expression of SOD and CAT mRNA in intestine and respiratory tree of A. japonicus (P< 0.05), except of the intestine of sea cucumber in 1.6% group. The supplement of Gin in diets exceed 1.2% can up-regulate the expression of CAT mRNA in intestine of A. japonicus (P< 0.05), and the expression of CAT mRNA in respiratory tree of A. japonicus significantly increased in 0.4%,0.8% and 1.2% groups. Those results indicated that the supplement of Gin in diets can improve the antioxidant capacity of sea cucumber by up-regulate the expression of SOD and CAT mRNA in the tissues of sea cucumber. However, the change patterns of the expression SOD and CAT mRNA were not contrary with activities of enzymes in some groups, indicating the negative feedback regulation of the secretion of enzymes on the gene expression. Sumnary, the suitable supplementation levels of Gin in diets of sea cucumber were 0.4%-0.8% under this experimental conditions.4. Effects of dietary n-3 highly unsaturated fatty acids (HUFAs) on growth, fatty aicd profiles,activity and gene expression of immune enzymes of sea cucumber Apostichopus japonicus (Selenka)Five experimental diets were prepared using S. thunbergii, soybean meal and fish meal as the main protein source and containing graded levels of n-3 HUFAs (0.46%, 0.85%,1.25%,1.61%å'Œ1.95%), and the 0.46% group was the control group. The specific growth rate, fatty acid profiles, activity and gene expression of immune enzymes of A. japonicus fed the 5 experimental diets were determined. It showed that the specific growth rate, activities of superoxide dismutase (SOD) and expression of SOD mRNA in the intestine and respiratory tree of A. japonicus all significantly increased when the levels of n-3 HUFAs in diets were over 0.85% compared to the control group (P<0.05). The the activities of CAT of sea cucumber significantly increased when the levels of n-3 HUFAs in diets were over 0.85% compared to the control group (P<0.05), and expression of CAT mRNA in the intestine of A. japonicus significantly increased in 0.85%,1.25% and 1.61% groups compared to the control group (P<0.05), and expression of CAT mRNA in the respiratory tree of A. japonicus significantly increased in 1.61% and 1.95% groups compared to control group (P<0.05). Those results indicated that the supplement of n-3 HUFAs in diets can improve activities SOD and CAT of by up-regulate the expression of SOD and CAT mRNA in the tissues of sea cucumber, and consequently improved the antioxidant capacity of sea cucumber. However, the change patterns of the expression SOD and CAT mRNA were not contrary with activities of enzymes in some groups, indicating the negative feedback regulation of the secretion of enzymes on the gene expression. The supplement of n-3 HUFAs in diets can significantly increase the contents of the EPA and DHA as the EPA and DHA contents of sea cucumber gradually increased with the increasing levels of n-3 HUFAs in diets. Sumnary, the suitable supplementation levels of n-3 HUFAs in diets of sea cucumber were 0.85%-1.25% under this experimental conditions.