饲料中蛋白脂肪比对斑点叉尾鮰幼鱼生长、消化酶活性及肌肉成分的影响

探讨了不同的蛋白和脂肪水平对斑点叉尾生长与品质等的影响,试验设计以豆粕调节蛋白含量,混合油脂(鱼油∶豆油=1∶1)调节脂肪含量,并以α-淀粉和次粉为填充物,共配制3个蛋白(P)水平(28%,32%,36%),每一蛋白水平设3个脂肪(L)水平(5.0%,7.5%,10.0%),共9种饲料,分别为P28L10,P32L10,P36L10,P28L7.5,P32L7.5,P36L7.5,P28L5,P32L5和P36L5,每组4重复,每重复80尾鱼[(1.5±0.02)g]。饲养60d后,进行生产性能测定,并采集肌肉等组织样本,测定相关指标。结果表明:饲料蛋白脂肪比对斑点叉尾幼鱼生长有显著影响(P<0.05)。其中P36L7.5组增重率(WGR)、饲料效率(FCR)最高,与P36L10和P32L7.5组差异不显著(P>0.05),但显著高于其它组(P<0.05)。P36L10组试验鱼肥满度(CF)最高,与P32L7.5和P36L7.5组差异不显著(P>0.05),但显著高于其他组(P<0.05)。鱼体内脏比(VBR)、腹脂率(MSI)随脂肪水平降低而显著降低(P<0.05)。试验各组肌肉水分含量差异不显著(P>...     

肌醇对哲罗鲑生长性能、体成分及消化酶活性的影响

为了探讨肌醇对哲罗鲑(Hucho taimen)生长性能、体成分及消化酶活性的影响, 以鱼粉、明胶和酪蛋白为蛋白源配制肌醇含量为99.8(不添加肌醇)、199.8、299.8、499.8、699.8、899.8和5 099.8 mg/kg的7种饲料, 分别投喂7个处理组, 每组3个重复, 每重复30尾鱼, 进行为期56 d的饲养实验。结果表明, 投喂肌醇含量为499.8 mg/kg饲料组的增重率最大, 且与添加量低于299.8 mg/kg的3个饲料组差异显著(P<0.05)。饲料系数在499.8 mg/kg饲料组最低, 在5 099.8 mg/kg饲料组最高, 两组间差异显著(P<0.05)。肌醇含量为499.8~899.8 mg/kg饲料组的特定生长率显著高于99.8~299.8 mg/kg及5 099.8 mg/kg饲料组(P<0.05)。肌肉中水分、粗脂肪和粗蛋白各组间差异不显著(P>0.05), 肝淀粉酶、幽门盲囊脂肪酶活性各组间差异不显著(P>0.05)。肠道蛋白酶活性在肌醇含量为199.8~499.8 mg/kg饲料组较高, 显著高于其他组(P<0.05), 脂肪酶活性在299.8~899.8 mg/kg饲料组高于99.8 mg/kg饲料组(P<0.05)。由此得出, 饲料中适量添加肌醇可提高哲罗鲑的生长性能及消化酶活性; 肌醇含量过低时哲罗鲑增重率、消化酶活性均较低; 肌醇含量过高时哲罗鲑特定增长率、消化酶活性较低, 饲料系数较高; 以增重率为指标由折线回归模型分析得出, 肌醇的最适含量为536.6 mg/kg饲料。

     

饲料蛋白质水平对拟穴青蟹幼蟹生长性能、体成分和消化酶活性的影响

用蛋白质水平分别为31.45%,36.37%,41.55%,46.13%,51.72%和56.86%的6种等能饲料,对初始体重为(11.86?0.11)mg的拟穴青蟹(Scylla paramamosain)幼蟹进行为期3周的养殖实验,考察饲料蛋白质水平对拟穴青蟹幼蟹生长性能、体成分以及消化酶活性的影响,以期获得拟穴青蟹幼蟹饲料蛋白质的适宜添加量。结果表明,饲料蛋白质水平对拟穴青蟹幼蟹的成活率影响不显著(P0.05);幼蟹的增重率和特定生长率随饲料蛋白质水平的提高先显著升高(P0.05)后稍有下降,最大值出现在蛋白质水平为51.72%的实验组;随着饲料蛋白质水平的提高,幼蟹粗蛋白质含量显著升高(P0.05)后趋于稳定,粗脂肪含量显著降低(P0.05),灰分含量先显著升高(P0.05)后显著降低(P0.05),水分含量则没有显著变化(P0.05);随着饲料蛋白质水平的提高,幼蟹蛋白酶活性显著升高(P0.05),淀粉酶活性显著降低(P0.05),各组脂肪酶活性也有显著差异(P0.05),但没有明显的变化规律。本研究条件下,饲料蛋白质水平在41.55%~56.86%,拟穴青蟹幼蟹均表现出较好的生长率,增重率和蛋白质水平的回归分析表明,幼蟹饲料蛋白质适宜水平为49.03%。     

小球藻对草鱼生长、免疫、消化酶活性和肌肉的影响

为探明饲料中添加不同水平的小球藻对草鱼生长性能、非特异性免疫机能、消化酶活性及肌肉品质的影响,选用平均体质量(105.92±2.79) g的草鱼随机分为5个组,每组30尾,分别投喂添加小球藻为0(对照组)、0.25%、0.50%、0.75%和1.00%的试验饲料,饲养周期为28 d。试验结果显示,0.50%、0.75%和1.00%添加组的终末平均体质量、质量增加率和特定生长率均显著高于对照组(P<0.05),饲料系数均显著低于对照组(P<0.05)。当添加量达0.75%时,能显著提高草鱼血清的溶菌酶和碱性磷酸酶的活性,增强草鱼的非特异性免疫机能(P<0.05)。各添加组血清中超氧化物歧化酶活性和抗氧化能力(除0.25%添加组)显著提高。各添加组草鱼脂肪酶和胰蛋白酶活性明显升高,淀粉酶(除0.25%添加组)活性显著减弱(P<0.05)。添加组草鱼肌肉的氨基酸组成与对照组无显著差异(P>0.05)。1.00%添加组的草鱼肌肉中亚麻酸和二十碳五烯酸含量显著高于对照组(P<0.05),0.25%、0.75%和1.00%添加组的花生四烯酸和二十二碳六烯酸含量显...     

胆汁酸对草鱼(Ctenopharyngodon idellus)的生长性能、肌肉营养成分及消化酶活性的影响

为研究胆汁酸对草鱼(Ctenopharyngodon idellus)生长性能、肌肉营养成分及消化酶活性的影响,选取初始体重为(13.11±0.58)g的草鱼540尾,随机分成6个实验组,分别饲喂胆汁酸添加量为0、75、150、225、300、375 mg/kg的等氮等能饲料(粗蛋白含量34.56％,总能13.54 kJ/g),养殖时间为60 d.结果显示,随着胆汁酸浓度的增加,草鱼的增重率(WGR)、特定生长率(SGR)均呈先上升后下降的变化趋势,且均在胆汁酸添加量为300 mg/kg时达到最大值(分别为281.18％和2.23％/d);饲料系数(FCR)则呈先下降后上升的趋势,且在胆汁酸添加水平为225 mg/kg时达最低值(1.26).由二次回归方程可知,WGR、SGR、FCR等生产性能最优时,胆汁酸添加水平分别为222.15、265.00、242.86 mg/kg.实验鱼肌肉粗脂肪含量随胆汁酸添加量的增加而呈先下降后趋于稳定的变化趋势,粗蛋白质含量则呈先上升后降低的变化趋势.肠道各段及肝胰脏的消化酶活性均随胆汁酸添加量的增加呈先升高后下降的趋势.由此说明,适量的胆汁酸能提高草鱼生长性能,促进其脂肪代谢,降低机体脂肪沉积,改善其肌肉品质.本研究考虑到草鱼消化酶活性、肌肉品质及生长性能等因素,其饲料中胆汁酸适宜的添加量为222.15-265.00 mg/kg.     

饲料中脂肪水平对方格星虫稚虫生长性能、体组成及消化酶活性的影响

以初始体重为15.50±0.04 mg的方格星虫稚虫为实验对象,分别饲喂脂肪水平为0.36％、3.32％、6.49％、9.31％、12.16％、15.14％和18.36％的7种等氮、等能饲料56 d,研究饲料脂肪水平对方格星虫稚虫生长、体组成及消化酶活性的影响.实验结果表明,(1)饲料脂肪水平对方格星虫稚虫的生长性能有显著影响(P＜0.05).随着饲料中脂肪水平的提高,方格星虫稚虫的增重率和特定生长率都呈先增后降的趋势,当饲料中脂肪水平为9.31％时,方格星虫稚虫增重率和特定生长率达到最大值.二次曲线回归分析确定当增重率达到极值时,饲料脂肪水平为8.70％;(2)饲料脂肪水平对方格星虫稚虫体组成中脂肪和蛋白质的含量影响显著(P＜0.05),方格星虫稚虫体脂肪含量随着饲料脂肪水平的上升有显著升高的趋势,18.36％组星虫体脂肪含量最高,显著高于0.36％、3.32％、6.49％、9.31％和12.16％组(P＜0.05).体蛋白含量随着饲料脂肪水平的上升有降低的趋势,18.36％组星虫的体蛋白含量最低,显著低于0.36％、3.32％、6.49％、9.31％和12.16％组(P＜0.05).饲料脂肪水平对方格星虫稚虫体组成中水分和粗灰分含量没有显著影响(P＞0.05);(3)随着饲料脂肪水平的增加,方格星虫稚虫蛋白酶活性和脂肪酶活性均呈先增后降的趋势,两种酶活性的最大值均出现在脂肪水平为9.31％时,但是饲料脂肪水平对方格星虫稚虫的淀粉酶活性没有显著的影响(P＞0.05).以增重率为评价指标时,方格星虫稚虫对饲料中脂肪的适宜需求量为8.70％.     

柠檬酸对罗非鱼生长、体成分和消化酶活性的影响

研究了饲料中添加不同水平柠檬酸 (0 .1%、0 .2 %、0 .3%、0 .4 % )对奥尼罗非鱼 (Oreochromisniloticus×O .aureus)幼鱼 (初始平均体重约 2 .0g)生长、饲料利用、体成分和消化酶活性的影响。共设 5组试验饲料 ,每一饲料组设 3个重复水族箱 ,每箱随机放鱼 15尾 ,投喂率为 6 % ,自然光周期 ,循环过滤水系统饲养 9周 ,每周称重 1次并相应调节投喂量。结果表明 :随着柠檬酸添加量的增大 ,饲料pH值呈下降趋势 ;添加 0 .2 %柠檬酸的试验组罗非鱼的特定生长率显著高于对照组 (P <0 .0 5 ,LSD多重比较 ,下同 ) ;饲料效率在 0 .3%柠檬酸组显著高于对照组 (P <0 .0 5 ) ;罗非鱼血清葡萄糖含量在0 .4 %组显著低于对照组、0 .1%组和 0 .3%组 (P <0 .0 5 ) ;0 .2 %组和 0 .3%组血清甘油三酯含量最高 ,但组间差异不显著(P >0 .0 5 ) ;全鱼水分、粗蛋白、粗脂肪和灰分含量在组间差异不显著 (P >0 .0 5 ) ;胃蛋白酶、胰蛋白酶和肠蛋白酶活性随柠檬酸添加量增加呈先上升后下降的趋势 ,0 .2 %组的最高 ,但组间差异不显著 (P >0 .0 5 ) ;肝胰脏和肠淀粉酶活性分别在 0 .2 %和 0 .3%组最高 ,组间差异亦不显著 (P >0 .0 5 )。结果提示 ,饲料中适量添加柠檬酸 ,能提高罗非鱼幼鱼消化酶活性 ,提高饲料利用率 ,促进罗非鱼生长     

饲料中添加枯草芽孢杆菌对拟穴青蟹幼蟹生长性能、消化酶活性和体成分的影响

为探讨饲料中添加不同含量枯草芽孢杆菌对拟穴青蟹(Scylla paramamosain)幼蟹生长、消化酶活性及体成分的影响,以初始体质量为(25.74±0.51)mg的拟穴青蟹Ⅰ期仔蟹为试验对象,在基础饲料中分别添加0、0.1%和0.5%的枯草芽孢杆菌制成3种试验饲料,饲喂幼蟹3周。试验结果:添加枯草芽孢杆菌的组,拟穴青蟹幼蟹的终末平均体质量、体质量增长率、特定生长率和蛋白酶活性显著高于对照组(P<0.05),但两个不同添加量试验组间的差异不显著(P>0.05);添加枯草芽孢杆菌显著增强了幼蟹蛋白酶和淀粉酶的活性(P<0.05),对幼蟹的水分、粗蛋白和灰分含量均没有显著影响(P>0.05);添加0.5%枯草芽孢杆菌的试验组,幼蟹的脂肪含量显著高于其它试验组(P<0.05)。结果表明,在本试验条件下,饲料中添加枯草芽孢杆菌对拟穴青蟹幼蟹的生长有显著促进作用,对蛋白酶活性、淀粉酶活性和体粗脂肪含量也有显著影响,添加0.1%～0.5%的枯草芽孢杆菌对拟穴青蟹幼蟹有较好的促生长效果。     

饲料蛋白水平对鳜鱼实验种群胃肠道消化酶活性的影响

探讨了饲料蛋白水平(ω蛋白)分别为29.8％,35.6％,45.7％和54.8％对鳜鱼体内4种消化酶活性的影响。结果表明,4种消化酶活性随饲料中ω蛋白水平的提高而增强,ω蛋白水平至45.7％时,4种酶的活性最高,其后,再随饲料中ω蛋白水平的提高,其活性有所下降。同时在各实验组中也发现,类胰蛋白酶的活性最高,其次为胃蛋白酶,再次为淀粉碎和纤维素酶,且淀粉酶和纤维素酶的活性相近,这可能与淀粉酶和纤维素酶都为分解多糖类物质有关。     

不同饵料对胭脂鱼生长和肠道消化酶活性的影响

研究了不同饵料(卤虫、饲料、水蚯蚓、水蚯蚓+饲料)对胭脂鱼生长和消化酶活性的影响。在水温(18±2)℃将初始体质量为(6.60±0.40)g的胭脂鱼随机分成4组,每组3个重复,每个重复放养10尾鱼,分别饲喂卤虫、饲料、水蚯蚓、水蚯蚓+饲料,试验周期56d。试验结果表明,水蚯蚓+饲料混合组和水蚯蚓组生长效果最佳,混合组优于水蚯蚓组(P0.05),饲料组和卤虫组次之,饲料组优于卤虫组(P0.05);肠道消化酶活性卤虫组饲料组水蚯蚓组混合组,卤虫组和饲料组3种消化酶活性均最低,水蚯蚓组与水蚯蚓+饲料混合组差异显著(P0.05)。     

Effects of dietary supplementation of fructooligosaccharide on growth performance,body composition,intestinal enzymes activities and histology of blunt snout bream (Megalobrama amblycephala) fingerlings

A feeding trial was conducted to investigate the effects of dietary fructooligosaccharide (FOS) on growth performance, body composition, intestinal enzymes activities and histology of fingerling Megalobrama amblycephala. A total of 1200 fish (1.42 ± 0.01 g) were fed diets containing graded levels of FOS (0, 0.5, 1, 2, 4 and 8 g kg⁻¹ diet) for 8 weeks in a recirculating system indoor. The weight gain, specific growth rate (SGR) and survival rate were all improved in dietary supplementation of FOS fed fish. Increasing FOS levels resulted in both higher whole‐body lipid and lower moisture contents, whereas ash and protein contents showed no significant differences among all the treatments. Intestinal amylase, protease, Na⁺, K⁺‐ATPase, alkaline phosphatase, γ‐glutamyl transpeptidase and creatine kinase activities all increased with dietary FOS levels up to 4 g kg⁻¹ (P < 0.05). Transmission electron microscopy analysis indicated that microvilli length in the mid‐intestine was significantly increased with increased dietary FOS levels (P < 0.05). In conclusion, dietary supplementation of FOS could confer benefits on growth performance, intestinal digestive and absorptive ability, histology of fingerling Megalobrama amblycephala.     

Effects of dietary carbohydrate/lipid ratios on growth performance,body composition and glucose metabolism of fingerling blunt snout bream Megalobrama amblycephala

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 ± 0.03 g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10 weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P < 0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P > 0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P < 0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P < 0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P < 0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P > 0.05) among all the treatments, while liver glycogen content increased significantly (P < 0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose‐6‐phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second‐order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4 g kg⁻¹, respectively, with a corresponding dietary CHO/L ratio of 3.58.     

Effects of dietary choline supplementation on growth performance,lipid deposition and intestinal enzyme activities of blunt snout bream Megalobrama amblycephal fed high‐lipid diet

This study aimed to investigate the effects of dietary choline supplementation on growth, lipid deposition and intestinal enzyme activities of Megalobrama amblycephala. Fish were fed four diets with two lipid levels (50 and 150 g kg^?1) and two choline supplementations (600 and 1600 mg kg^?1) for 8 weeks. Feed conversion ratio (FCR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF) ratio, whole‐body and muscle lipid contents, intestinal lipase activities and lipoprotein lipase (LPL) activities all increased significantly (P < 0.05) as lipid levels increased, whereas the opposite was true for whole‐body and muscle moisture contents and intestinal amylase activities. VSI, IPF ratio and whole‐body lipid contents all decreased significantly (P < 0.05) with increasing dietary choline supplementations. Weight gain, muscle moisture content all increased significantly (P < 0.05) with increasing dietary choline supplementations when dietary lipid levels reached 150 g kg^?1, whereas the opposite was true for FCR, IPF ratio, IPF and liver LPL activities. In addition, abnormal hepatocytes were found in the liver of fish fed 150 g kg^?1 lipid with 600 mg kg^?1 choline supplementation. The result of this study indicated that extra choline supplementation can improve growth performance, intestinal enzymes activities and reduce excessive lipid deposition of M. amblycephala fed high lipid.     

Effects of dietary tryptophan levels on growth performance,whole body composition and gene expression levels related to glycometabolism for juvenile blunt snout bream,Megalobrama amblycephala

To investigate the effects of dietary tryptophan on growth and glycometabolism in juvenile blunt snout bream, 450 fish (initial weight 23.33 ± 0.03 g) were fed six practical diets with graded levels of tryptophan (from 0.79 g/kg to 5.96 g/kg dry matter) for 8 weeks. Results showed that final weight, per cent weight gain (PWG), protein efficiency rate, feed intake and feed conversion ratio (FCR) were significantly improved by 2.80 g/kg diet. The maximum values of protein and ash were observed in 2.80 g/kg diet, while moisture was minimum. Lipid content of fish fed 3.95 g/kg diet was significantly higher than other diets. The highest plasma insulin‐like growth factor‐1 (IGF‐1) content was observed in 0.79 g/kg diet. In the liver, IGF‐1 mRNA levels were significantly downregulated by 2.80 g/kg dietary tryptophan, while glucokinase levels were by 3.95 g/kg, while glucose‐6‐phosphatase and phosphoenolpyruvate carboxykinase mRNA levels showed a converse trend compared with IGF‐1. Based on PWG and FCR, the optimal dietary tryptophan level was determined to be 1.99 g/kg (6.20 g/kg of dietary protein) and 1.96 g/kg (6.11 g/kg of dietary protein), respectively, using broken‐line regression analysis.     

Dietary biotin requirement of juvenile blunt snout bream,Megalobrama amblycephala

This study was conducted to determine the optimal dietary biotin requirement of juvenile Megalobrama amblycephala. Quadruple groups of fish (initial average weight 2.01 ± 0.01 g) were fed thrice daily with six isonitrogenous and isoenergetic purified diets containing 0 (basal diet), 0.015, 0.049, 0.158, 0.624 and 2.49 mg kg^?1 biotin, respectively, for 8 weeks. Results showed that survival rate, final weight, feed intake, specific growth rate, protein efficiency ratio and nitrogen retention efficiency all increased significantly (P < 0.01) as dietary biotin levels increased from 0 to 0.049 mg kg^?1, whereas the opposite was true for feed conversion ratio. Dressout percentage, condition factor, hepatosomatic index, viscera/body ratio all showed no significant difference (P > 0.05) within the biotin range tested. Contrary to moisture content, whole‐body protein and lipid contents showed a positive correlation with dietary biotin levels. In addition, liver biotin content increased significantly (P < 0.05) with increasing dietary biotin levels up to 0.624 mg kg^?1. Hepatic pyruvate carboxylase (PC) and acetyl‐CoA carboxylase (ACC) activities both showed an increasing trend as dietary biotin levels increased. Based on the regression analysis of weight gain, hepatic PC and ACC activities, the optimal dietary biotin requirement of juvenile Megalobrama amblycephala is estimated to be 0.063, 0.071 and 0.075 mg kg^?1, respectively.     

甘草次酸对团头鲂生长、脂肪沉积与抗氧化功能的影响

为探讨甘草次酸对团头鲂生长、脂肪沉积和抗氧化功能的影响,选取均体质量为(15.63±0.04)g的团头鲂幼鱼420尾,随机分在15个网箱中,分别以甘草次酸水平为0、0.15、0.30、0.45和0.60 g/kg的5种饲料投喂8周。结果发现,饲料添加甘草次酸对团头鲂增重率、特定生长率、饵料系数没有显著影响(P0.05)。甘草次酸可以显著降低实验鱼脏体比、肝体比、腹脂率及肝脏脂肪含量(P0.05),但对全鱼体组成和肌肉脂肪含量无显著影响(P0.05)。比对血浆脂肪代谢酶可见,0.30~0.60 g/kg甘草次酸添加组血浆总胆固醇含量较对照组显著下降(P0.05);而甘油三酯、游离脂肪酸和高密度脂蛋白胆固醇含量无显著变化(P0.05)。肝脏中脂蛋白酯酶、肝酯酶和总酯酶活性在添加甘草次酸后显著降低(P0.05);0.30~0.60 g/kg甘草次酸添加组脂肪酶活性显著高于其他各组(P0.05)。饲料添加甘草次酸可以显著提高肝脏超氧化物歧化酶活性和还原型谷胱甘肽含量,降低丙二醛含量(P0.05)。研究表明,饲料中添加0.30~0.45 g/kg甘草次酸时,显著降低了团头鲂内脏团的脂肪沉积,改善了鱼体脂肪分布,这可能是由于甘草次酸加强脂解作用,提高脂肪代谢酶活性导致的;饲料中添加甘草次酸也可显著提高团头鲂的抗氧化能力。     

团头鲂营养需求与健康研究进展

团头鲂是我国主要的大宗淡水养殖品种之一,其养殖规模在近10年不断扩大。团头鲂的营养物质需求主要以生长和营养缺乏症为评价指标。而营养物质对鱼类健康,如免疫反应和抗病力等影响的研究尚不充分。一般认为,饲料中营养物质搭配合理、品质优良有利于维持鱼类生理健康,并能保护养殖水环境。此外,一些营养物质如维生素,在鱼类的免疫机制中发挥重要作用。未来水产饲料应具有促进水产动物生长和维持健康的双重作用,通过营养调控预防鱼类疾病是保证水产养殖可持续发展的重要策略之一。本研究综述了团头鲂对蛋白质、脂肪、碳水化合物、维生素和矿物质营养需求的研究进展,以及饲料营养元素对团头鲂免疫力及抗病力影响的最新报道,以期为团头鲂高效配合饲料的开发提供科学参考。     

Dietary histidine affects intestinal antioxidant enzyme activities,antioxidant gene expressions and inflammatory factors in juvenile blunt snout bream (Megalobrama amblycephala)

Six semipurified diets of graded histidine levels (from 4.1 to 14.2 g/kg) were fed to fish for 8 weeks. The results showed that the intestinal content of malondialdehyde (MDA), activities of total superoxide dismutase (T‐SOD) and glutathione peroxidase (GPx) were noticeably lower in 8.0 g/kg diet compared to control group. While the lowest activities of copper–zinc superoxide dismutase (Cu/Zn‐SOD) and manganese superoxide dismutase (Mn‐SOD) were observed in 9.9 g/kg diet, the intestinal activities of total antioxidant capacity (T‐AOC) and catalase (CAT) in 14.2 g/kg diet were noticeably higher than those in 8.0 and 9.9 g/kg diets. Plasma biochemical indexes were not significantly affected by dietary histidine levels. In the intestine, the Kelch‐like ECH‐associated protein 1 (Keap1) mRNA levels were increased in 8.0 g/kg diet, which suppressed the nuclear translocation of nuclear factor E2‐related factor 2 (Nrf2), and subsequently decreased CAT, GPx1, Cu/Zn‐SOD and Mn‐SOD expression levels. The lowest mRNA levels of interleukin 8 (IL‐8) and tumour necrosis factor‐α (TNF‐α) were observed in 8.0 g/kg diet, whereas the highest mRNA levels of transforming growth factor‐β (TGF‐β) and interleukin 10 (IL‐10) were observed in 8.0 g/kg diet. These results indicated that dietary histidine plays a major role in maintaining intestinal health in juvenile blunt snout bream.     

Dietary methionine requirement of juvenile blunt snout bream (Megalobrama amblycephala) at a constant dietary cystine level

A 9‐week feeding trial was conducted to investigate the dietary methionine requirement of juvenile Megalobrama amblycephala at a constant dietary cystine level. Six semipurified diets were formulated to contain graded dietary methionine levels from 3.9 to 15.4 g kg^?1 in about 2.5 g kg^?1 increments in the presence of 2.2 g kg^?1 cystine. Results showed that specific growth rate (SGR) and protein efficiency ratio (PER) significantly increased with increasing dietary methionine levels from 3.9 to 12.4 g kg^?1 and thereafter kept stable. Maximum protein productive value (PPV), nitrogen retention efficiency (NRE) and liver weight were observed in 8.5 g methionine kg^?1 diet. Protein contents in whole fish body were positively correlated with dietary methionine level, while lipid contents were negatively correlated with it. Morphological index and hepatic glutamate‐pyruvate transaminase (GPT) activities were independent of dietary methionine levels. However, dietary methionine supplementation significantly improved haematological parameters, plasma methionine and total essential amino acid contents and hepatic glutamate‐oxaloacetate transaminase (GOT) activities. Analysis of dose response using broken‐line regression on the basis of SGR and PPV versus dietary methionine level estimated the optimum dietary methionine requirements of juvenile M. amblycephala to be between 8.5 and 8.4 g kg^?1 of diet (25.0 and 24.7 g kg^?1 of protein) in the presence of 2.2 g kg^?1 cystine, respectively. Hence, the corresponding total sulphur amino acids requirements of this species were calculated to be 10.7 and 10.6 g kg^?1 of diet (31.5 and 31.2 g kg^?1 of dietary protein).     

Effects of complete fish meal replacement by rice protein concentrate with or without lysine supplement on growth performance,muscle development and flesh quality of blunt snout bream (Megalobrama amblycephala)

An 8‐week feeding trial was conducted to evaluate the effects of fish meal (FM) replacement by rice protein concentrate (RPC) with supplementation of microcapsule lysine (ML) or crystalline lysine (CL) on growth performance, muscle development and flesh quality of blunt snout bream. Four isonitrogenous and isoenergetic diets were formulated, including FM diet (containing 50 g/kg FM), RPC diet (FM replaced by RPC), MRPC diet (FM replaced by RPC with ML supplementation) and CRPC diet (FM replaced by RPC with CL supplementation). Fish fed FM diet had significantly higher weight gain, feed efficiency, protein efficiency ratio and nitrogen and energy utilization than that of RPC group, but showed no statistical difference with other treatments. In addition, fish fed RPC diet showed higher muscle fibre frequency in the 20‐ to 50‐μm class but lower >50‐μm class and higher cooking loss than that of the other groups. Furthermore, no significant difference was found in whole‐body proximate compositions, frequency distribution of <20‐μm‐diameter fibres, texture, muscle content, collagen, pH 24 hr post‐mortem and sensory quality. The results showed that RPC supplemented with ML or CL could replace fishmeal without any adverse effects on growth performance and flesh quality for blunt snout bream.