Nutritional Physiology Of Lipid And Vitamin E In Black Seabream, Acanthopagrus Schlegeli

Black seabream Acanthopagrus schlegeli is a valuable commercial species for aquaculture in many parts of Asia.The objectives identified in the study are as follows:1.Effect of dietary protein to energy ratios on growth and body composition of juvenile black seabream,Acanthopagrus schlegeliA growth experiment was conducted to determine the optimal dietary protein to energy(P/E)ratio for juvenile black seabream,Acanthopagrus schlegeli.Twelve diets were formulated to contain four protein levels(34,38,42,46),each with three lipid levels(10,13,16),and a fixed carbohydrate level of 16%,using fish meal and soybean meal as 15rotein source,mixture of equally proportioned fish oil and soybean oil as lipid source.P/E ratios of the diets ranged from 96.76 to 136.21 mg protein.kcal^-1.960 juvenile black seabream(initial average weight 3.39±0.18 g)were randomly assigned to 12 groups,each had double replicate.The fish were reared in 24 tanks (0.75m×0.75m×1.2m)for 42 d.The results showed that specific growth rate(SGR), feed conversion ratio(FCR)were significantly better in fish fed with high protein diets(38,42,46)than those fed with low protein diets(34)(P＜0.05),and with middle and high lipid diets(13,16)than those fed with low lipid diets(10)(P＜0.05).No significant difference in percent survival was found among all groups(P＞0.05). Fish fed the diet whose protein and lipid level were 42%and 16%respectively had the best SGR(3.20),PER(2.10),FCR(1.14).Carcass lipid contents positively correlated with dietary lipid level.At the same protein level,body protein and ash content increased with increasing dietary lipid level.Statistical results suggest that the growth was significantly affected by P/E ratios of the diets(P＜0.05),lipid had a significant effect of protein sparing(P＜0.05).In conclusion,for juvenile black seabream,the best growth performance was produced when the protein level was 42%, lipid level was 16%and P/E ratio was 110.37 mg protein·kcal^-1.So,the diet containing 42%protein and 16%lipid with P/E ratio of 110.37 mg protein·kcal^-1is optimal for juvenile black seabream. 2.Dietary vitamin E requirement of juvenile black seabream,Acanthopagrus schlegeliA 9-week feeding experiment was conducted to evaluate the effects of dietary vitamin E levels on growth,nutritional composition,plasma composition,hepatic antioxidant enzyme activity and IGF-I mRNA expression of black seabream, Acanthopagrus schlegeli(initial weight,11.23±0.45g).Seven diets were formulated using fish meal and casein as protein source,mixture of equally proportioned fish oil and soybean oil as lipid source.Seven levels of vitamin E supplement at 0,50,100, 200,300,400 and 800 mgα-tocopherol acetate kg^-1diet were used.Each diet was assigned to triplicate groups.The results showed that dietary vitamin E levels significantly affected growth performance(P＜0.05),and the highest weight gain was harvested at the 155.86mg/kg vitamin E level.FCR followed similar trends as weight gain.HSI,CF and survival rate among different groups were not significantly affected by dietary vitamin E levels(P＞0.05).With the increase of dietary vitamin E level, the vitamin E contents of liver and muscle were both increased,while the hepatic MDA,plasma cholesterol and triacylglycerol contents were reduced.Dietary vitamin E significantly reduced the hepatic SOD and CAT activities,but no significant difference was found among groups in which dietary vitamin E levels changed from 42.5 to 380.91 mg/kg(P＞0.05).The increased dietary vitamin E levels significantly increased the hepatic IGF-I mRNA expression,and the highest expression was received at vitamin E level of 155.86 mg/kg.In conclusion,dietary vitamin E level could significantly affect growth of black seabream,the increased dietary vitamin E increased the antioxidant capacity,inhibited lipid peroxidation and promoted hepatic IGF-I mRNA expression.Broken-line analysis of weight gain on concentrations of dietary vitamin E indicates that the optimal vitamin E levels for maximal growth of juvenile black seabream was 139.27mg/kg.3.Effect of dietary oxidized fish oil on growth,lipid peroxidation and liver histology of juvenile black seabream,Acanthopagrus schlegeliThe aim of the present study was to determine the impact of oxidized fish oil in diets for black seabream(Acanthopagrus schlegeli)on growth,lipid peroxidation in liver and hepatic histology.Two isonitrogenous and isocalofic diets were formulated utilizing fresh fish oil(peroxide value,1.27meq·kg^-1oil)and oxidized fish oil (peroxide value,45meq·kg^-1oil)as the lipid source respectively and the diet prepared with fresh fish oil served as control.The fish was fed to apparent satiation twice a day for 63 days.Each diet was assigned to triplicate groups,and each group was stocked with 30 juveniles with an initial weight of 18.6 g.Weight gain,feed efficiencies and protein efficiency ratios of the fish fed the diet containing oxidized fish oil were significantly lower than those fed the control diet(P＜0.05).The protein content of carcass of the fish fed the diet containing oxidized fish oil was significantly reduced (P＜0.01).There was a significant effect of oxidized fish oil on the lipid content in the liver and muscle(P＜0.05).However,no effect on moisture and protein contents in liver and muscle was observed(P＞0.05).The hepatic peroxidation was measured by thiobarbituric acid reactive substances(TBARS).TBARS values were higher for fish fed the diet containing oxidized fish oil than those fed the control diet(P＜0.05), but the hepatic VE content was significantly reduced by the dietary oxidized fish oil(P＜0.05).Additionally,Hepatic superoxide dismutase(SOD)and Catalase(CAT) activities in fish fed the diet adding oxidized fish oil were also significantly increased (P＜0.05).Histologically,fish fed the diet containing oxidized fish oil showed foci of hepatocytes with enlarged irregular nuclei located at the periphery of the cell,and some lipidic vacuoles in the cytoplasm.The present results suggest that growth performance of juvenile black seabream can be affected seriously by oxidized fish oil. The TBARS values and histological changes observed suggest an impact of oxidized fish oil on the transport or metabolism of fat in the fish which requires further investigation.4.The compensatory effects of dietary vitamin E on biochemical indices of juvenile black seabream(Acanthopagrus schlegeli)fed oxidized oilA 9-week feeding experiment was conducted to evaluate the effects of dietary vitamin E supplementation on growth,lipid peroxidation,plasma chemical composition,hepatic antioxidant enzyme activity and fatty acid composition of black seabream(Acanthopagrus schlegeli)fed oxidized oil.Two basal diets containing either fresh oil(FL)or oxidized oil(OL)were formulated.Within the OL basal diet, five levels of vitamin E supplement at 0,100,300,700,and 1500 mgα-tocopherol acetate kg^-1diet were used,giving a total of six experimental diets.Fish were hand-fed to apparent satiation twice daily.At end of the trial,the weight gain and survival rate of fish were significantly reduced by diets with oxidized oil,while hepatosomatic index was remarkably high in fish fed oxidized oil diet.However, vitamin E supplementation to diet significantly improved growth performance and increased vitamin E content in the liver.Significant(P＜0.05)inter-treatment differences in whole body fat content were examed,but no differences in liver and muscle fat content were noted(P＞0.05).Plasma cholesterol and triacylglycerol contents were significantly reduced by vitamin E supplementation,but no significant difference in plasma cholesterol and triaeylglycerol contents among vitamin E supplemented groups.Catalase(CAT),superoxide dismutase(SOD)and glutathione-S-transferase(GST)activities in fish liver were all significantly reduced by dietary vitamin E supplementation(P＜0.05),and with the increase of vitamin E supplementation,CAT and SOD activities were also reduced.In contrast,glutathione peroxidase(GPX)and glutathione reductase(GR)were less affected by the dietary vitamin E supplementation(P＞0.05).Although,liver thiobarbituric acid-reactive substances and docosahexaenoic acid were significantly increased by dietary oxidized oil,their levels were reduced by dietary vitamin E supplementation.Our results indicate that vitamin E supplementation at＞100 mgα-tocopherol acetate kg^-1diet could reduce lipid peroxidation and improve fish growth performance when oxidized oils exist in diet.5.Effects of dietary n-3 HUFA and VE levels on growth and biochemical indices of juvenile black seabream,Acanthopagrus schlegeliThe aim of the present study was to determine the impact of n-3 HUFA and vitamin E levels in diets for black seabream(Acanthopagrus schlegeli)on growth, nutritional composition,biochemical indices in the liver and plasma.Twelve diets were formulated to contain three vitamin E levels(0,200,600 mgα-tocopherol acetate/kg diet)and each with four n-3 HUFA levels,using fish meal and soybean meal as protein source,mixture of different proportioned fish oil and coconut oil as lipid source.Different amounts of fish oils were mixed with different amounts of coconut oil to adjust the n-3 HUFA in diets.Each diet was randomly assigned to triplicate groups of juvenile black seabream(initial weight,21.48±0.15g).Fish were fed twice daily to apparent satiation for 9 weeks.The results showed that weight gain was significantly increased with the increase of dietary n-3 HUFA.Weight gain of low vitamin E level(0mg/kg,diets 3 and 4)were significantly lower than those of middle (200 mg/kg)and high(600 mg/kg)vitamin E levels(diets 7,8 and diets 11,12), respectively.However,no significant difference in weight gains among middle and high vitamin E levels.FCR followed similar trends as weight gain.Dietary vitamin E level did not significantly affect the HSI,CF and survival rate(P＞0.05).The increased n-3 HUFA in diets reduced the lipid contents of whole body and muscle. With the increase of n-3 HUFA in diets,vitamin E contents significantly reduced (except low vitamin E level),while hepatic MDA contents significantly increased. However,among middle and high vitamin E levels in diets,no significant difference was found at the same n-3 HUFA levels.The increased n-3 HUFA levels in diets significantly increased hepatic PUFA contents except low vitamin E level.Likewise, the increased vitamin E levels in diets increased hepatic PUFA and n-3 HUFA contents.The increased n-3 HUFA in diets increased the requirement of vitamin E for black seabream,and the n-3 HUFA and vitamin E levels had a significant synergistic effect on hepatic vitamin E,EPA,DHA,PUFA and n-3 HUFA(P＜0.05).With the increase of n-3 HUFA in diets,plasma cholesterol,triacylglycerol,HDL and LDL contents increased,while the increased vitamin E did not significantly affect plasma cholesterol and triacylglycerol contents.Dietary n-3 HUFA levels did not significantly affect plasma SOD and CAT activities(P＞0.05).The increased vitamin E levels in diets significantly reduced plasma SOD and CAT activities(P＜0.05),while no significant difference among middle and high vitamin E levels.In conclusion,dietary n-3 HUFA and vitamin E levels had a significant synergistic effect on growth performance of black seabream,and under our study condition,for black seabream, the best growth performance was harvested when vitamin E level in diet was about 130mg/kg,n-3 HUFA was about 12%(%total lipid).6.Effect of high dietary vegetable oils on growth,chemical composition and antioxidant capacity of juvenile black seabream,Acanthopagrus schlegeliA 9-week feeding experiment was carded out on juvenile black seabream, Acanthopagrus schlegeli(initial weight 20.26±0.22 g)to evaluate effects of dietary replacement of fish oil by vegetable oils on growth and tissue biochemical composition.Triplicate groups of fish were hand fed with seven iso-nitrogenous, iso-calorific,iso-lipidic experimental diets,in which 60%,80%and 100%of fish oil were replaced by soybean oil(diets 60SO,80SO,100SO)or mixed vegetable oils (soybean oil,rapeseed oil and linseed oil)(60Mix,80Mix,100Mix),respectively.The diet containing 100%fish oil was control diet(FO).The inclusion of 60%vegetable oils in diets showed higher weight gain,similar to fish fed FO diet.However,80% fish oil replacement reduced the fish grouth,but not significantly.Weight gains of fish fed 80Mix and 100Mix diets were higher than those of fish fed 80SO and 100SO diets, respectively.No significant differences were found in hepatosomatic index,feed conversion ratio,whole body and liver proximate composition among experimental diets,although there was a trend for liver fat to increase with fish oil replacement.The inclusion of vegetable oils in diets increased hepatic a-tocopherol concentrations, whereas reduced thiobarbituric acid-reactive substances values and plasma total cholesterol levels.Concentrations of saturated and monounsaturated fatty acid were highest in livers of fish fed FO diet,whereas polyunsaturated fatty acids were higher in SO and Mix diets.Linoleic acid and linolenic acid significantly increased in fish fed SO and Mix diets(P＜0.05).The contents of docosahexaenoic acid, eicosapentaenoic acid and the ratio n-3/n-6 were significantly reduced by dietary vegetable oils(P＜0.05).Plasma SOD and CAT activities were reduced by dietary vegetable oils,and the low activities of SOD and CAT were both occurred between 60-80%fish oil replacement.Dietary vegetable oil increased hepatic GSH content, but not significantly.The present study indicated that fish oil can be replaced up to 60-80%by vegetable oils in black seabream diets for a period of 9 weeks without negatively affecting fish performance.7.Effect of dietary L-carnitine on growth and tissue biochemical composition of juvenile black seabream,Acanthopagrus schlegeliThe effects of dietary L-camitine on growth,nutritional composition,plasma chemical composition and liver fatty acid composition of black seabream were investigated.The basal diet was formulated using fish meal and soybean meal as protein source,mixture of fish oil and vegetable oil(soybean oil,rapeseed oil and linseed oil)as lipid source.Three levels of L-eamitine supplement at 0,300 and 1000 mg/kg diet were used,giving a total of three experimental diets(LC0,LC300 and LC1000).Each diet was randomly assigned to triplicate groups of juvenile black seabream(initial weight,20.42±0.24g).Fish were fed twice daily to apparent satiation for 9 weeks.The results showed that dietary L-carnitine did not significantly affect growth,FCR and survival rate of black seabream(P＞0.05).Dietary L-carnitine supplement reduced HSI and CF,but not significantly(P＞0.05).The moisture content of liver was significantly reduced by dietary L-carnitine(P＜0.05).The liver lipid content in LC1000 diet was significantly reduced by dietary L-camitine,but no significant difference was found between LC300 and LC0 diets.With the increase of dietary L-camifine,plasma HDL and LDL were reduced.Plasma cholesterol and triacylglycerol contents were reduced by dietary L-camifine,and the cholesterol and triacylglycerol contents in LC1000 diet were significantly lower than those in LC0 diet(P＜0.05).Dietary L-camitine did not significantly affect hepatic SFA and MUFA contents,but significantly increased PUFA content(P＜0.05).The present study indicated that,under our experimental condition,dietary L-camitine did not promote the growth performance of black seabream,but had some effects to reduce the lipid of the fish.