Studies on the Fatty Liver Diseases of Sciaenops ocellatus Caused by Different Ether Extract Levels in Diets

An experiment was conducted to study fatty liver disease caused by different ether extract levels in diets of juvenile Sciaenops ocellatus. Juvenile S. ocellatus (n=1,260; initial body weight approximately 2.73 g) were divided into nine treatment groups (triplicate groups per treatment) and fed in aquatic cases by a recirculated filtered rearing system; the temperature of the aquatic cases was maintained at 23.2±2.0° for 8 weeks. Nine kinds of diets containing different protein (38, 42, 46%) and ether extract levels (4, 8, 12%) were used. Results showed that the relative growth ratio and survival ratio of the fish fed on medium lipid diets (8%) or high ether extract diets (12%) were significantly lower than those of the fish fed on low ether extract diets (4%) (p < 0.05). There was a positive correlation between the ether extract contents in hepatopancreas of fish and the ether extract contents of diets. At the end of the experimental period, the fish of the nine experimental groups suffered from different degrees of fatty liver disease and serious illness, and death occurred in a large number of fish fed on medium (8%) and high ether extract diets (12%) from the third test week; mortality was highest in the fifth test week. The ill S. ocellatus showed symptoms of loss of appetite, lack of movement, black skin, and weight loss and eventually died. The main pathological change in ill fish was fatty liver disease. Their hepatopancreas were swollen and pale, accompanied by fatty degeneration, fatty necrosis of hepatocytes, and atrophy of the pancreas. Ultrastructural changes showed the presence of many lipid droplets and granules in the mitochondria, endoplasmic reticulum, and cell plasm of hepatocytes. Study results indicated that all the nine kinds of diets with different lipid or protein levels could cause nutritional fatty liver disease in juvenile S. ocellatus. The pathological severity and serious level of fatty liver disease in the tested fish positively correlated with the contents of the ether extract, but not with those of protein, in test diets. The increase in the level of ether extract in test diets was responsible for the direct cause of illness or death in juvenile S. ocellatus. Translated from Acta Hydrobiologica Sinica, 2005, 29(1) (in Chinese)     

饵料中不同脂肪水平诱导红姑鱼脂肪肝病的研究

1260尾初始重约为273g的红姑鱼(Sciaenopsocellatus)分为9组,每组3个平行,用9种不同水平蛋白质与脂肪日粮饲养于循环水系统的水泥池网箱内,在水温为232±20℃条件下养殖56d。本实验为饵料中不同脂肪水平诱导红姑鱼脂肪肝病的研究。9种日粮中蛋白质含量分别为:36%,40%,44%;脂肪含量分别为:4%,8%,12%。红姑鱼的各期生长率和存活率随着日粮脂肪含量增加而显著下降,红姑鱼肝胰脏脂肪含量与日粮脂肪水平成正比,各组红姑鱼均发生程度不同的营养性脂肪肝病,其病变程度与日粮脂肪水平成正相关。饲喂脂肪含量分别为8%,12%日粮的红姑鱼从实验3周起开始大量发病死亡,死亡率在5周达到高峰。主要表现为厌食,不游动,皮肤发黑,消瘦直至死亡。解剖见肝胰脏肿大,苍白发黄,柔软易碎。组织学检查发现,各组红姑鱼肝胰脏均见肝细胞不同程度的脂肪变性,溶解坏死,胰腺细胞亦萎缩。电子显微镜观察,在肝细胞线粒体、内质网与细胞浆内有大量微细至大颗粒状的脂滴出现。实验结果表明,饲喂9种不同水平的蛋白质和脂肪日粮的红姑鱼均引起营养性脂肪肝病,其病变程度与日粮脂肪水平成正相关,日粮中脂肪是红姑鱼发病与死亡的直接原因。       

Influence of dietary conjugated linoleic acid (CLA) on lipid and fatty acid composition in liver and flesh of Atlantic salmon (Salmo salar)

The aim of the present study was to determine the effects of conjugated linoleic acid (CLA) on lipid and fatty acid metabolism in Atlantic salmon. The overall objective being to test the hypotheses that CLA has beneficial effects in salmon including growth enhancement, improved flesh quality through decreased adiposity and lipid deposition thereby minimising detrimental effects of feeding high fat diets, and increased nutritional quality through increased levels of beneficial fatty acids including n-3 highly unsaturated fatty acids (HUFA) and CLA itself. Salmon smolts were fed diets containing two levels of fish oil (low, approximately 18% and high, approximately 34%) containing three levels of CLA (a 1:1 mixture of 9-cis,trans-11 and trans-10,cis-12. at 0, 1 and 2% of diet) for 3 months and the effects on growth performance, liver and muscle (flesh) lipid contents and class compositions, and fatty acid compositions determined. The diets were also specifically formulated to investigate whether the effects of CLA, if any, were more dependent upon absolute content of CLA in the diet (as percentage of total diet) or the relative level of CLA to other fatty acids. Dietary CLA in salmon smolts had no effect on growth parameters or biometric parameters. However, there was a clear trend of increased total lipid and triacylglycerol contents in both liver and flesh in fish fed CLA, particularly in fish fed the high oil diets. Finally, CLA was incorporated into tissue lipids, with levels in flesh being 2-fold higher than in liver, but importantly, incorporation in liver was at the expense of saturated and monounsaturated fatty acids whereas in flesh it was at the expense of n-3HUFA.     

Dietary vitamin E supplementation affects tissue lipid peroxidation of hybrid tilapia,Oreochromis niloticus x O. aureus

A feeding trial was conducted to evaluate the effects of dietary vitamin E contents on the growth, ascorbate induced iron-catalyzed lipid peroxidation in post-mortem muscle and liver tissue, and Raman spectral changes in lens of juvenile hybrid tilapia (Oreochromis niloticus x O. aureus). Experimental fish were fed practical diets supplemented with 0, 50, 100, 200, 450 and 700 mg alpha-tocopheryl acetate/kg diet for 14 weeks. There was no significant difference in weight gain, feed conversion ratio and protein efficiency ratio among fish fed test diets (P>0.05). Protein content of fish fed diet containing the lowest vitamin E level was the lowest (P<0.05) among all groups. No difference was found in other body constituents among test fish (P>0.05). The thiobarbituric acid-reactive substances produced by iron-catalyzed lipid peroxidation in muscle and liver tissue of fish fed the diet without alpha-tocopheryl acetate supplementation were significantly (P<0.05) greater than those from fish fed diets containing higher levels of alpha-tocopheryl acetate. Dietary vitamin E supplementation increased the antioxidant capability of tilapia tissues against lipid peroxidation. Further, dietary vitamin E supplementation also influenced the lens cortical membrane structure of tilapia.     

共轭亚油酸对草鱼肝脏和肌肉组织的细胞学形态、抗氧化能力以及脂肪代谢相关基因表达的影响

采用65d的生长实验研究共轭亚油酸(CLA)对草鱼肝脏和肌肉细胞学形态、抗氧化能力以及脂肪代谢相关基因表达的影响。共配制7种近似等氮(粗蛋白: 36 g/100 g)等脂(粗脂肪: 4.5 g/100 g)的饲料: 0 (对照组)、0.5 (CLA0.5)、1 (CLA1)、1.5 (CLA1.5)、2 (CLA2)、2.5 (CLA2.5)和3 g/100 g CLA (CLA3)。每个饲料组均设置3个生物学重复,实验鱼初始体重约为(5.08±0.08) g。实验结果显示:与对照组相比,CLA0.5-CLA2.5组草鱼肝脏和肌肉组织细胞学形态均无明显异常,但CLA3组肝细胞线粒体空泡化,内质网肿胀,排列过于紧密;肌细胞肌节结构松散,肌原纤维降解;在CLA1.5-CLA2.5组肝脏和肌肉中超氧化物歧化酶(SOD)、总抗氧化能力(T-AOC)和谷胱甘肽过氧化物酶(GPx)活力均显著上升(P<0.05);在CLA1.5-CLA3组中肝脏过氧化氢酶(CAT)活力均显著高于对照组(P<0.05),但谷胱甘肽还原酶(GR)活力无显著变化(P>0.05),且在CLA0.5-CLA3组中肌肉CAT和GR活力均无显著变化(P>0.05)。CLA1.5-CLA2组肝脏中MDA含量显著低于对照组(P<0.05),而CLA2.5-CLA3组MDA含量显著高于对照组(P<0.05)。CLA3组肌肉中MDA含量显著高于对照组(P<0.05)。与对照组相比,在CLA1.5-CLA2.5组肝脏和肌肉中乙酰辅酶A羧化酶(ACC) mRNA表达显著下调(P<0.05),脂蛋白脂酶(LPL)、激素敏感性脂肪酶(HSL)和过氧化物酶体增殖物激活受体α(PPARα)均显著上调表达(P<0.05)。在CLA2-CLA3组肝脏以及CLA1.5-CLA2和CLA3组肌肉中脂肪酸去饱和酶2(FAD2)mRNA显著上调表达(P<0.05)。过氧化物酶体增殖物激活受体γ(PPARγ)mRNA在CLA1-CLA3组肝脏中显著下调表达(P<0.05),而其在肌肉中均无显著变化(P>0.05)。综上所述,结合2%CLA在不影响草鱼的生长和饲料利用,且显著降低肝脏脂肪积累,研究结果建议,2% CLA在不影响草鱼肝脏和肌肉组织细胞学形态的前提下,可有效提高其肝脏和肌肉组织抗氧化能力并促进其脂肪分解代谢以及抑制脂肪合成代谢相关基因表达。     

Effects of dietary hydrolysate supplementation on growth,body composition,hematological responses,and liver histology of juvenile giant trevally (Caranx ignobilis Forsskal, 1775)

A feeding study was conducted to investigate how fish protein hydrolysate (FPH) supplementation affected the growth, feed utilization, body composition, and hematology of juvenile giant trevally (Caranx ignobilis Forsskal, 1775). Seven isonitrogenous (52% protein) and isocaloric diets (10% lipid) were formulated, wherein shrimp hydrolysate (SH) and tuna hydrolysate (TH) were used to replace fishmeal at inclusion levels of 0 (control), 30, 60, and 90 g/kg and labeled as control, SH30, SH60, SH90, TH30, TH60, and TH90, respectively. Each diet was fed to triplicate groups of juvenile giant trevally for 8 weeks. The results showed higher final body weight and specific growth rate in fish fed SH30, SH60, TH30, and TH60 than fed control diet. No difference was observed in feed intake, but reduced feed conversion ratio (FCR) was found in fish fed SH30, SH60, TH30, and TH60, demonstrating these diets improved feed utilization. TH90 caused deposition of lipid droplet in the hepatocyte, a sign of liver damage. Total monounsaturated fatty acids, polyunsaturated fatty acids (PUFA), and highly unsaturated fatty acids in fish were not affected by FPH supplementation. Fish fed TH30 showed lower ∑n − 3 PUFA than the fish fed remaining dietary treatments. The elevated serum protein was seen in fish fed control, SH30, SH60, and TH30, demonstrating that these diets were beneficial for the innate immune response in giant trevally. The results indicate that TH and SH could be incorporated into diets of giant trevally at 30–60 g/kg, replacing 7%–13% fishmeal with enhanced growth and health benefits.     

4 种不同脂肪源对太平洋鲑生长和体组成的影响

在日粮中添加11.5%的4 种不同来源脂肪饲养180 尾初始重约为110g 的太平洋鲑(Oncorhynchus spp.)于水泥池中56d。实验分4 组,每组3个平行池,每池15尾鱼。研究日粮中4 种不同来源脂肪对淡水养殖太平洋鲑生长性能、体组成与品质的影响。4 组脂肪源分别为鱼油(实验1 组)、大豆油(实验2 组)、大豆磷脂(实验3 组)和玉米油(实验4 组)。实验表明:(1) 实验各组太平洋鲑存活率相似,但大豆磷脂组的特定生长率显著好于鱼油组、大豆油组和玉米油组(P0.05)。大豆磷脂组、大豆油组和玉米油组的饲料效益显著好于鱼油组(P< 0.05); (2) 大豆油组、大豆磷脂组和玉米油组太平洋鲑肠系膜脂肪与肝脏脂肪含量不同程度低于鱼油组,而肌肉中脂肪含量不同程度低于鱼油组; (3) 实验各组太平洋鲑肝脏脂肪、肌肉脂肪和肠脂中总多不饱和脂肪酸组成基本相似,但玉米油组、大豆磷脂组和大豆油组太平洋鲑总n-3 多不饱和脂肪酸比例较鱼油组显著下降,而总n-6 系多不饱和脂肪酸比例显著提高(P<0.05);(4) 玉米油组、大豆磷脂组和大豆油组太平洋鲑血浆中脂肪分解酶、甘油三酯和高密度脂蛋白指标较鱼油组不同程度上升;(5) 实验各组太平洋鲑解剖组织学检查未见异常病理变化。实验结果表明,淡水养殖条件下,太平洋鲑日粮中脂肪以添加大豆磷脂的生长性能最好,大豆油、玉米油和鱼油效果相似,添加玉米油、大豆磷脂和大豆油均不影响太平洋鲑健康状况和品质。       

Fish oil reduces cholesterol and arachidonic acid content more efficiently in rats fed diets containing low linoleic acid to saturated fatty acid ratios

Rats were fed diets containing a high level of saturated fatty acids (hydrogenated beef tallow) versus a high level of linoleic acid (safflower oil) at both low and high levels of fish oil containing 7.5% (w/w) eicosapentaenoic and 2.5% (w/w) docosahexaenoic acids for a period of 28 days. The effect of feeding these diets on the cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding diets high in fish oil with safflower oil decreased the cholesterol content of rat serum, whereas feeding fish oil had no significant effect on the cholesterol content of serum when fed in combination with saturated fatty acids. The serum cholesterol level was higher in animals fed safflower oil compared to animals fed saturated fat without fish oil. Consumption of fish oil lowered the cholesterol content of liver tissue regardless of the dietary fat fed. Feeding diets containing fish oil reduced the arachidonic acid content of rat serum and liver lipid fractions, the decrease being more pronounced when fish oil was fed in combination with hydrogenated beef tallow than with safflower oil. These results suggest that dietary n-3 fatty acids of fish oil interact with dietary linoleic acid and saturated fatty acids differently to modulate enzymes of cholesterol and fatty acid metabolism.     

The effects of dietary (n-3) fatty acid supplementation on lipid dynamics and composition in rat lymphocytes and liver microsomes

Rats were fed diets devoid of (n-3) fatty acids (olive oil supplementation) or high in (n-3) fatty acids (fish oil supplementation) for a period of 10 days. In spleen lymphocytes and liver microsomes derived from animals fed fish oil diets, relatively high levels of (n-3) eicosapentaenoic (20:5), docosapentaenoic (22:5) and docosahexaenoic acids (22:6) were obtained compared to minimal levels when fed the olive oil diet. When the average lipid motional properties were examined by measuring the fluorescence anisotropy of diphenylhexatriene, no significant different was found between intact liver microsomes from animals fed the two diets. However, when lipid motion was examined in vesicles of phosphatidylcholine, isolated from the microsomes from fish oil fed animals (21.4% (n-3) fatty acids), the fluorescence anisotropy was significantly less than the corresponding phosphatidylcholine from olive oil fed animals (5.6% (n-3) fatty acids), indicating a more disordered or fluid bilayer in the presence of higher levels of (n-3) fatty acids. Phosphatidylethanolamine (n-3) fatty acids were also elevated after fish oil supplementation (41.3% of total fatty acids), compared to the level after olive oil supplementation (21.4%). The major effect of the fish oil supplementation was a replacement of (n-6) arachidonic acid by the (n-3) fatty acids and when this was 'modeled', using liposomes of synthetic lipids, 1-palmitoyl-2-arachidonyl(n-6) or docosahexaenoyl(n-3)-phosphatidylcholine, significant differences in lipid motional properties were found, with the docosahexaenoate conferring a more disordered or fluid lipid environment. Thus it appears that although lipid order/fluidity can be significantly decreased by increases in the highly unsaturated (n-3) fatty acid levels, alterations in membrane domain organization and/or phospholipid molecular species composition effectively compensated for the changes, at least as far as average lipid motional properties in the intact membranes was concerned.     

Effects of varying levels of dietary vitamin E (α‐tocopherol) on growth performance,proximate and fatty acid composition of juvenile silver pomfret (Pampus argenteus Euphrasen, 1788)

This study investigated the effects of elevated dietary levels of vitamin E (α‐tocopherol) on growth performance, proximate composition and fatty acid profiles of juvenile silver pomfret, Pampus argenteus. Three semi‐purified experimental diets were formulated to contain 49% protein and 16% lipid. High docosahexaenoic acid (DHA) tuna oil was added to the diets to supplement DHA. A graded level of vitamin E (0‐, 50‐, and 100 mg kg^?1) was added to experimental diets 1 to 3, respectively. Analyzed vit. E levels were 155.2, 195.3 and 236.4 mg kg^?1 in diets 1, 2 and 3, respectively. The experiment was conducted for 12 weeks with juvenile silver pomfret (29.6 ± 7.6 g) using a flow‐through system consisting of nine 1‐m³ tanks. Each treatment had three replicates and fish were stocked at the rate of 20 m^?3. Growth performance and feed utilization parameters of fish fed diets 2 and 3 were significantly (P < 0.05) higher than in fish fed diet 1, but the parameters in diets 2 and 3 did not differ significantly (P > 0.05). Although whole body protein levels were not influenced by the dietary vit. E levels, whole body lipid in fish fed diet 2 was significantly higher than in fish fed the other diets. The whole body vit. E levels in fish fed diet 2 (22.6 mg kg^?1) and diet 3 (24.1 mg kg^?1) were significantly (P < 0.05) higher than in those fed diet 1 (18.2 mg kg^?1). Whole body total saturated fatty acids were significantly lower, and DHA levels higher in fish fed diets 2 and 3 than those fed diet 1. The results of the present study suggest that increasing dietary supplementation of vit. E in high lipid diets enhances the growth performance of fish and that a dietary level of 196 mg kg^?1 vit. E is suitable for the growth of silver pomfret.     

Suppression of fatty acid synthase by dietary polyunsaturated fatty acids is mediated by fat itself,not by peroxidative mechanism

This study examined the effect of dietary polyunsaturated fatty acids (PUFA) that were supplemented with vitamin E on lipid peroxidation, glutathione-dependent detoxifying enzyme system activity, and lipogenic fatty acid synthase (FAS) expression in rat liver. Male Sprague-Dawley rats were fed semipurified diets containing either 1% (w/w) corn oil or 10% each of beef tallow, corn oil, perilla oil, and fish oil for 4 wk. Alpha-tocopherol was supplemented in perilla oil (0.015%) and fish oil (0.019%). Hepatic thiobarbituric acid reactive substances, an estimate of lipid peroxidation, were not significantly different among the dietary groups. The glutathione peroxidase, glutathione reductase, and glutathione S-transferase activities were all elevated by the polyunsaturated fats, especially fish oil. The activity of FAS was reduced in the polyunsaturated fat-fed groups in the order of fish oil, perilla oil, and corn oil. The mRNA contents decreased in rats that were fed the 10% fat diets, particularly polyunsaturated fats, compared with the rats that were fed the 1% corn oil diet. Similarly, the inhibitory effect was the greatest in fish oil. These results suggest that lipid peroxidation can be minimized by vitamin E; PUFA in itself has a suppressive effect on lipogenic enzyme.     

Fatty acid composition and lipid peroxidation of soft-shelled turtle, Pelodiscus sinensis, fed different dietary lipid sources

Juvenile soft-shelled turtles (Pelodiscus sinensis) were fed 7 diets containing 8% of lard, soybean oil, olive oil, menhaden fish oil, or mixtures of 1 to 1 ratio of fish oil and lard, soybean oil, olive oil for 10 weeks. Growth and muscle proximate compositions of the turtles were not affected by different dietary treatments (p>0.05). Fatty acid profiles in muscle polar lipids, muscle non-polar lipids, and liver polar lipids reflected the fatty acid composition of dietary lipid source. Turtles fed diets containing fish oil generally contained significantly higher (p<0.05) proportion of highly unsaturated fatty acids (HUFA) in both polar and non-polar lipids of muscle and polar fraction of liver lipids than those fed other oils. Non-polar fraction of liver lipids from all groups of turtles contained less than 1% of HUFA. All turtles contained relatively high proportions of oleic acid in their lipids regardless of the dietary lipid source. Further, lipid peroxidation in both muscle tissue and liver microsomes of turtles fed fish oil as the sole lipid source was greater (p<0.05) than those fed fish oil-free diets. Turtles fed olive oil as the sole lipid source had the lowest lipid peroxidation rate among all dietary groups. The results indicate that dietary n-3 HUFA may not be crucial for optimal growth of soft-shelled turtles although they may be used for metabolic purpose. Further, high level of dietary HUFA not only increases the HUFA content in turtle tissues, but also enhances the susceptibility of these tissues to lipid peroxidation.     

Effects of thermal stress and vitamin C on lipid peroxidation and fatty acid composition in the liver of thornfish Terapon jarbua

The effects of thermal stress and vitamin C were examined on the lipid peroxidation and fatty acid composition in the liver of thornfish. Small thornfish were cultured at 28, 32 and 36 degrees C and then fed diets with 0, 80, 400 and 2000 ppm vitamin C-supplement, respectively, for 8 weeks. Fish fed a diet without vitamin C supplement and cultured at 36 degrees C showed the highest values of hepatosomatic index and malondialdehyde, followed by fish fed a diet without vitamin C supplement and cultured at 32 degrees C. Lipid peroxidation in the liver of fish was elevated by high water temperature and prevented by vitamin C. The % of polyunsaturated fatty acid (PUFA) in the liver lipid was higher when fish were cultured at the lower water temperature. Vitamin C significantly reduced the % of PUFA and increased the % of saturated fatty acid (SFA) in the liver lipid. The % of SFA in the liver lipid was not affected by water temperature. We conclude that temperature and vitamin C significantly affected the lipid characters of liver in thornfish.     

Effect of diets containing sesame oil on growth and fatty acid composition of rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate effects of fish oil replacement by sesame oil in combination with other vegetable oils in diets with regard to growth performance, feed utilization, desaturation and elongation, whole fish and liver fatty acid profiles of juvenile rainbow trout. Sesame oil (SO) used in the feeds was a mixture of linseed (LO), sunflower (SFO) and fish oil (FO), whereas the control diet contained only FO. Duplicate groups of 60 rainbow trout (~7 g) held under similar culture conditions were fed 2% of their body weight per day for 75 days. At the end of feeding trials, there was no difference in feed utilization efficiency or growth performance between the control group and the groups with added sesame oil (P > 0.05). However, viscerosomatic and hepatosomatic index values were significantly higher (P < 0.05) in fish fed with FO30/SO35/SFO35 diets. Results showed that total body lipid levels of fish fed diets containing sunflower oil were higher than in the other experimental groups (P < 0.05). However, crude lipid levels were similar in fish fed the control diet and the diet with sesame oil (FO30/LO35/SO35), which is sunflower oil‐free. Crude lipid levels of fish livers were not influenced by the diets (P > 0.05). Diets with sesame oil increased desaturation and elongation of 18 : 3n‐3 towards n‐3 HUFA. The conclusion was that the diet addition of sesame oil in combination with other vegetable oils increased the nutritional quality of the whole fish and liver of juvenile rainbow trout, in particular the docosahexaenoic acid (DHA) level. Therefore, sesame oil may be of interest for use in aquaculture.     

Effect of dietary conjugated linoleic acid (CLA) on lipid composition, metabolism and gene expression in Atlantic salmon (Salmo salar) tissues

Dietary conjugated linoleic acid (CLA) affects fat deposition and lipid metabolism in mammals, including livestock. To determine CLA effects in Atlantic salmon (Salmo salar), a major farmed fish species, fish were fed for 12 weeks on diets containing fish oil or fish oil with 2% and 4% CLA supplementation. Fatty acid composition of the tissues showed deposition of CLA with accumulation being 2 to 3 fold higher in muscle than in liver. CLA had no effect on feed conversion efficiency or growth of the fish but there was a decreased lipid content and increased protein content after 4% CLA feeding. Thus, the protein:lipid ratio in whole fish was increased in fish fed 4% CLA and triacylglycerol in liver was decreased. Liver beta-oxidation was increased whilst both red muscle beta-oxidation capacity and CPT1 activity was decreased by dietary CLA. Liver highly unsaturated fatty acid (HUFA) biosynthetic capacity was increased and the relative proportion of liver HUFA was marginally increased in salmon fed CLA. CLA had no effect on fatty acid Delta6 desaturase mRNA expression, but fatty acid elongase mRNA was increased in liver and intestine. In addition, the relative compositions of unsaturated and monounsaturated fatty acids changed after CLA feeding. CLA had no effect on PPARalpha or PPARgamma expression in liver or intestine, although PPARbeta2A expression was reduced in liver at 4% CLA feeding. CLA did not affect hepatic malic enzyme activity. Thus, overall, the effect of dietary CLA was to increase beta-oxidation in liver, to reduce levels of total body lipid and liver triacylglycerol, and to affect liver fatty acid composition, with increased elongase expression and HUFA biosynthetic capacity.     

Dietary lipid level influences fatty acid profiles, tissue composition, and lipid peroxidation of soft-shelled turtle, Pelodiscus sinensis

Dietary lipids containing equal portions of soybean oil and fish oil were fed to juvenile Chinese soft-shelled turtle, Pelodiscus sinensis, at supplementation level of 0 to 15% for 8 weeks. Tissue fat contents of turtles increased when dietary lipid concentration increased. Fatty acid profiles for turtles fed diets supplemented with 6% or higher levels of lipids were similar to those in dietary lipids. On absolute value basis, fatty acids of 14-, 16-, and 18-carbons in muscle of turtles fed diet without lipid supplementation were higher than those in the initial turtle muscle. Among them, C16:1 and C18:1 was approximately 4 and 2 fold higher, respectively, than that of the initial turtles. By contrast, absolute amounts of C20:5 and C22:6 in muscle of turtles fed diet without lipid supplementation were slightly less than those in the initial turtles. For turtles fed lipid supplemented diets, tissue C20:5 and C22:6, however, increased when dietary lipid level increased. These results suggest that soft-shelled turtles are capable of synthesizing fatty acids up to 18 carbons from other nutrients and that they may have limited or no ability to synthesize highly unsaturated fatty acids. Lipid peroxidation measured by thiobarbituric acid-reactive substances in tissues of turtles fed 12% and 15% lipids was greater (p<0.05) than that in turtles fed 3% to 9% lipids. This could be due to high lipid and unsaturated fatty acid content in these tissues. On lipid basis, lipid peroxidation in turtles fed diet without lipid supplementation was the highest among all groups suggesting the existence of antioxidant factors in the dietary lipids.     

Dietary lipid requirement on non-specific immune responses in juvenile grass carp (Ctenopharyngodon idella)

This study aimed to evaluate the dietary lipid requirement and its effects on liver oxidative status and non-specific immune responses of juvenile grass carp (Ctenopharyngodon idella). Purified diets with five dietary lipid levels (0%, 2.5%, 5%, 7.5% and 10%, fish oil/corn oil = 1:1) were each fed to triplicate groups of grass carp (mean initial weight: 6.57 ± 0.01 g) in a recirculating rearing system maintained at 27.5 ± 0.5 °C for 10 weeks. Percent weight gain was highest (P < 0.05) with 5% lipid and lowest in fish fed the lipid free control diet. Feed efficiency (FE) and protein efficiency ratio (PER) in fish followed the same pattern of percent weight gain. Fish fed with lipid containing diets had better non-specific immune response indexes (e.g. phagocytic activity, plasma peroxidase and lysozyme activity) and low-level of liver oxidation status than fish fed with the control diet. But excess dietary lipid supplement would bring over metabolic burden to liver. After the feeding trial, fish were challenged by Aeromonas hydrophila. Fish fed control diet obtained significantly (P < 0.05) lower survival rate. The survival rate was highest with 7.5% lipid. The results of this study indicated that proper dietary lipid supplementation enhanced the immune response of grass carp and improved the survival rate in the bacterial challenge, but excess dietary lipid may elevate liver oxidation rates of grass carp. Analysis by second-order regression of percent weight gain indicated that the optimal dietary lipid level in juvenile grass carp (6.6–35.5 g) is about 6.5%.     

Dietary oligonucleotides from yeast RNA influence immune responses and resistance of hybrid striped bass (Morone chrysops x Morone saxatilis) to Streptococcus iniae infection

Three feeding trials were conducted to evaluate potential immunomodulatory effects of nucleotides in the diet of hybrid striped bass. A basal diet was formulated from menhaden fish meal to contain 40% crude protein and 10% lipid. An oligonucleotide product (Ascogen P) from brewer's yeast was added to the basal formulation at the manufacturer's recommended rate of 0.5% to produce the experimental diet. Each diet was fed to four replicate groups of juvenile hybrid striped bass for seven or eight weeks in two separate trials. After Trials 1 and 2, a Streptococcus iniae bath challenge was executed to test the effects of diet on disease resistance. No significant difference in growth performance was observed between fish fed the basal and experimental diets. Body composition of whole fish, hematocrit and serum lysozyme levels were observed to be within normal ranges and not influenced by dietary nucleotides. Neutrophil oxidative radical production of fish fed the nucleotide-supplemented diet was significantly (P=0.011) higher than in fish fed the basal diet. Significantly (P<0.05) enhanced survival after exposure to S. iniae also was generally observed in fish fed the nucleotide-supplemented diet. In addition, fish fed the nucleotide-supplemented diet tended to have a higher antibody response based on microtitration agglutination; however, the difference was not statistically significant because of high variation between individual fish. Long-term (16 weeks) administration of oligonucleotides in Trial 3 failed to show enhancement of immune responses between treatments. It is concluded that dietary oligonucleotides positively influenced immune responses and resistance of juvenile hybrid striped bass to S. iniae infection.