饲料蛋白质水平与投喂频率对吉富罗非鱼幼鱼生长及部分生理生化指标的影响

为探讨饲料蛋白质水平与投喂频率对罗非鱼生长及生理健康的影响,采用2×3双因子实验,研究饲料蛋白质水平(36.27%和26.02%)与投喂频率(1、2和3次/d)对吉富罗非鱼幼鱼生长、体成分、血清指标和肝胰脏结构的影响。养殖周期为42 d,结果表明:随饲料蛋白质水平的增加,实验鱼的末体质量(FW)、增重率(WGR)、特定生长率(SGR)、饲料效率(FE)、肥满度(CF)、去内脏全鱼灰分(EWA)、内脏水分(VM)、高密度脂蛋白胆固醇(HDLC)水平显著升高(P0.05),而摄食率(FI)、脏体比(VSI)、饲料成本(FC)、去内脏全鱼粗脂肪(EWF)、内脏粗脂肪(VF)、肝胰脏粗脂肪(HF)显著降低(P0.05);随投喂频率的增加,实验鱼的FW、WGR、SGR、肝体比(HSI)、CF、FC、EWF、VF、HF,血清中的总胆固醇水平(TCHO)、HDLC、低密度脂蛋白胆固醇(LDLC)、总蛋白(TP)、甘油三酯(TGK)水平显著升高(P0.05),而FE、蛋白质效率(PER)、去内脏全鱼水分(EWM)、EWA、VM、肝胰脏水分(HM)显著降低(P0.05)。饲料蛋白质水平和投喂频率对实验鱼的FW、WGR、SGR、VM和HDLC的交互作用显著(P0.05)。投喂26.02%蛋白质水平饲料的实验鱼,肝胰脏细胞肿大变形,呈现透明的空泡化,出现细胞核偏移;而投喂36.27%蛋白质饲料的实验鱼,大多数肝细胞胞浆清晰,可观察到的肝细胞空泡面积较小。综合考虑,饲料蛋白质含量为36.27%是适合吉富罗非鱼幼鱼的,其适宜的投喂频率为2次/d以上,可根据罗非鱼市场情况进行调节。     

投喂频率对池塘循环水养殖大口黑鲈消化酶、组织结构及脂代谢酶基因表达的影响

为研究池塘工程化循环水养殖模式下投喂频率(2 次/d、3 次/d、4 次/d)对大口黑鲈(Micropterus salmoides)体成分、肠道消化和肝脏组织结构及脂蛋白酯酶(LPL)和肝脂酶(HL)基因相对表达丰度的影响, 选用平均体重为 (5.0±0.4) g 的大口黑鲈为研究对象, 在池塘工程循环水养殖系统中进行为期 120 d 的养殖实验。结果表明, 投喂频率对鱼体全鱼的粗脂肪和灰分含量影响显著(P<0.05); 投喂频率 2 次/d 组的灰分含量显著高于其他两组, 而 2 次/d 组体脂肪含量低于投喂 3 次/d、4 次/d 组, 体水分和粗蛋白含量均不受投喂频率的影响(P>0.05); 投喂频率 2 次/d 组肠道淀粉酶和脂肪酶活性显著高于 4 次/d 投喂组(P<0.05); 投喂频率对大口黑鲈肠道绒毛高度和宽度影响不显著 (P>0.05), 4 次/d 组肠道绒毛排列整齐度下降且肌层厚度显著低于 2 次/d 和 3 次/d 组(P<0.05)。肝脏组织学显示, 投喂频率越高肝脏脂肪堆积加重, 相对于 2 次/d 和 3 次/d 组, 4 次/d 组肝细胞偏移、空泡化的现象较明显。在第 60 天和 90 天, 2 次/d 组 LPL 基因相对表达量显著高于 4 次/d 组(P<0.05); 而在第 120 天时, LPL 的相对表达量在各组间差异不显著(P>0.05)。2 次/d 组 HL 基因相对表达量显著高于 4 次/d 组(P<0.05)。综合分析, 在饱饲投喂条件下, 池塘循环水养殖大口黑鲈的适宜投喂频率为 2 次/d。     

大菱鲆幼鱼对饲料中泛酸最适需求量的研究

为研究大菱鲆(Scophthalmus maximus)幼鱼对泛酸的最适需求量，在基础配方中添加不同梯度的泛酸钙，制成6组泛酸含量分别为6.24、10.64、15.02、23.81、41.40和76.57 mg/kg等氮等能实验饲料，投喂初始体重为(24.73±0.10) g的大菱鲆幼鱼80 d。结果显示：1)泛酸对幼鱼成活率(SR)无显著影响(P>0.05)，10.64~76.57 mg/kg饲料组增重率(WGR)和特定生长率(SGR)显著提高(P< 0.05)；泛酸含量超过23.81 mg/kg时，肝体比(HSI)显著降低(P<0.05)；2)随着饲料中泛酸含量的提高，全鱼粗蛋白、粗脂肪和肌肉粗蛋白均呈先升后降趋势，肝脏脂肪含量显著下降(P<0.05)；3)肠道消化酶、Na+, K+-ATPase和肝脏胆碱酯酶(ChE)活力随泛酸添加量的增加呈先上升后下降趋势，10.64~76.57 mg/kg饲料组肠道肌酸激酶(CK)活力显著提高(P<0.05)；4)血清、肝脏中过氧化氢酶(CAT)、超氧化物歧化酶(SOD)活力均呈先升后降趋势；6.24 mg/kg饲料组血清丙二醛(MDA)含量显著高于其他5组(P<0.05)；5)随泛酸含量的增加，肝脏脂肪合成酶(FAS)基因表达量先升后降，脂蛋白酯酶(LPL)基因表达量显著上升(P<0.05)。研究表明，饲料中添加适宜的泛酸能显著增强大菱鲆幼鱼肠道消化、吸收能力和机体抗氧化能力，并可提高脂肪代谢相关基因的表达水平，从而提高其生长性能。以增重率为判据，经折线模型拟合得出，初体重为24.73 g的大菱鲆幼鱼对泛酸的需求量为16.08 mg/kg饲料。     

投喂频率对绿鳍马面鲀幼鱼生长和肌肉品质的影响

为研究不同投喂频率对绿鳍马面鲀幼鱼生长性能和肌肉品质的影响,在室内循环水养殖系统中,采用人工配合饲料,以1次/d、2次/d、3次/d、4次/d等4种投喂频率,对体质量(13.8±0.83)g的绿鳍马面鲀幼鱼进行了饲养试验,试验时长为42 d。结果显示,随着投喂频率增加,绿鳍马面鲀幼鱼的终末体质量呈逐渐升高的趋势,特定生长率呈先升后降的变化趋势,其中3次/d组幼鱼的特定生长率最高,显著高于1次/d组(P<0.05);饲料系数也随着投喂频率的增加而升高,3次/d组的饲料系数显著高于1次/d组(P<0.05),4次/d组的饲料系数显著高于1次/d组和2次/d组(P<0.05);肌肉品质方面,4次/d组幼鱼的肌肉粗脂肪含量显著高于1次/d组(P<0.05),不同投喂频率组间肌肉粗蛋白质含量和灰分含量无显著性差异(P<0.05)。综合考虑生长性能和肌肉品质指标,绿鳍马面鲀幼鱼适宜的投喂频率为日投3次。     

饲料脂肪水平对克氏原螯虾幼虾生长性能及肌肉品质的影响

本研究旨在探讨饲料脂肪水平对克氏原螯虾(Procambarus clarkii)幼虾生长性能和肌肉品质的影响。实验选取600尾初始体重为(4.00±1.00) g的克氏原螯虾幼虾，随机分为5组(L1、L2、L3、L4和L5组)，分别投喂脂肪水平为2.86%、5.11%、7.67%、10.19%和13.02%的等氮实验饲料，养殖周期为60 d。结果显示，随着脂肪水平的升高，特定生长率(SGR)呈先升高后降低的趋势(P<0.05)，饲料系数(FCR)呈先降低后升高的趋势(P<0.05)，L3组的FCR显著低于其余组(P<0.05)；对SGR进行折线回归分析，得出最适脂肪含量为6.82%。饲料脂肪水平对克氏原螯虾肌肉的水分、粗蛋白和粗灰分含量无显著影响(P>0.05)；随着饲料脂肪水平的增加，肌肉的蒸煮损失率、粗脂肪含量、总多不饱和脂肪酸(∑PUFA)和总氨基酸(∑TAA)含量呈上升趋势，L5组的二十碳五烯酸(EPA)显著高于其余组，L5组的二十二碳六烯酸(DHA)含量显著高于L1和L2组(P<0.05)；随着饲料脂肪水平的增加，肌肉硬度、弹性、凝聚性和黏性呈下降趋势，且L1~L3组间均无显著差异(P>0.05)，L5组的总鲜味氨基酸(∑FAA)、丙氨酸(Ala)及天门冬氨酸(Asp)的含量显著低于L1组(P<0.05)。综上所述，适宜的饲料脂肪含量可以提高克氏原螯虾幼虾的生长性能和肌肉的营养品质，在本实验条件下，克氏原螯虾幼虾饲料中脂肪的建议添加量为6.82%~10.19%。     

小麦蛋白粉替代鱼粉对大黄鱼幼鱼生长、血清生化指标及抗氧化能力的影响

为研究小麦蛋白粉替代大黄鱼幼鱼饲料中的鱼粉对其生长性能、体成分、血清生化指标及肝脏抗氧化能力的影响,实验以小麦蛋白粉替代基础饲料中0%(FM组为对照组)、25%(WGM25组)、50%(WGM50组)、75%(WGM75组)和100%(WGM100组)的鱼粉,配制成5种等氮(蛋白质水平为45%)等脂(脂肪水平为10%)的饲料。结果显示,大黄鱼幼鱼各处理组的存活率(SR)和饲料系数(FCR)差异不显著;增重率(WGR)和特定生长率(SGR)各替代组显著高于对照组;各处理组的肝体比(HSI)、脏体比(VSI)和肥满度(CF)差异不显著。全鱼粗蛋白、粗脂肪、水分和灰分的含量差异不显著;肌肉粗蛋白、粗脂肪、水分含量差异不显著;肌肉灰分含量WGM50、WGM75组和FM、WGM25、WGM100组差异显著。各处理组大黄鱼血清中谷丙转氨酶(ALT)、谷草转氨酶(AST)的含量均无显著性差异。肝脏超氧化物歧化酶(SOD)的活性,WGM25和WGM100组显著低于FM、WGM50和WGM75组;丙二醛(MDA)的活性,WGM50组显著高于FM、WGM25和WGM100组;过氧化氢酶(CAT)的活性,各组间差异不显著;谷胱甘肽过氧化物酶(GPx)的活性,WGM100组显著高于其他组。研究表明,在该实验条件下,小麦蛋白粉替代饲料(含40%鱼粉)中100%的鱼粉不会影响大黄鱼幼鱼的生长。     

大鳞鲃幼鱼对脂肪的适宜需要量研究

为了解大鳞鲃(Barbus capito)幼鱼脂肪的需求量。试验分为5组,分别饲喂脂肪水平为3.92%(L1)、6.25%(L2)、8.36%(L 3)、10.75%(L4)、和12.91%(L5)的等氮等能饲料,养殖56 d后采样。结果显示:当饲料中脂肪水平从3.92%到8.36%逐渐增多时,鱼体增重率(WG)和特定生长(SGR)显著升高,饵料系数(FCR)明显降低;当饲料中脂肪含量继续增加时,鱼体WG和SGR呈下降趋势,FCR数则相反,且当饲料中脂肪水平为12.91%时,鱼体WG和FCR与饲料脂肪水平为8.36%时差异显著。大鳞鲃形体指标受饲料脂肪水平显著影响,其中,脏体比(VSI)随着饲料脂肪含量的升高而上升,而肝体比(HSI)却呈降低趋势,且当饲料中脂肪水平分别为10.75%和12.91%时,大鳞鲃幼鱼HSI显著低于对照组。饲料脂肪水平对全鱼、胴体和内脏的水分、粗蛋白和粗灰分显著影响较小,但仍能看出当饲料脂肪水平为6.25%时,全鱼的粗蛋白显著低于其他四组;全鱼、胴体和内脏的粗脂肪含量随饲料中脂肪水平的增加而上升,而肝脏中粗脂肪含量的变化趋势则相反,呈下降趋势。此外,以饲料中脂肪含量为自变量,分别以WG和FCR为因变量进行二次回归方程分析可得,大鳞鲃幼鱼WG最大时对脂肪的最适需求量为7.99%,而大鳞鲃幼鱼FCR最小时对脂肪的最适需求量为8.76%。综上可知,大鳞鲃幼鱼对饲料中脂肪的适宜需求量为7.99%~8.76%。     

饲料中添加L-肉碱对吉富罗非鱼生长、肝脏脂肪代谢及抗氧化能力的影响

分别在3组等氮等能的吉富罗非鱼(GIFT,Oreochromis niloticus)饲料中添加不同水平的L-肉碱[0(对照组)、150和300 mg/kg],试验选用初始体重为(8.21±0.33)g的幼鱼投喂9周,探讨L-肉碱对吉富罗非鱼生长、体成分、血清生化指标、肝脏脂肪代谢酶活性和抗氧化能力的影响。结果表明:添加150或300 mg/kg L-肉碱显著提高了罗非鱼增重率(WGR)和特定生长率(SGR),显著降低了实验鱼肝体比(HSI)和脏体比(VSI);添加150 mg/kg L-肉碱组WGR和SGR最高,HSI和VSI最低。添加150 mg/kg L-肉碱显著提高了鱼体肥满度(CF)。饲料系数(FCR)和存活率(SR)在对照组和实验组间无显著差异。添加150或300 mg/kg L-肉碱显著提高了鱼体肝脏中粗蛋白含量,添加150 mg/kg L-肉碱显著降低了肝脏粗脂肪含量。添加150或300 mg/kg L-肉碱时,血清甘油三酯(TG)含量显著降低,肝脏脂蛋白脂酶(LPL)、肝脂酶(HL)、总酯酶(LPL)和脂肪酶(LPS)活性显著上升,肝脏过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GSH-PX)活性显著增加,肝脏丙二醛(MDA)含量显著下降。添加300 mg/kg L-肉碱显著提高了鱼体肝脏超氧化物歧化酶(SOD)活性和溶菌酶(LZM)活性。综上,饲料中添加适量L-肉碱对提高吉富罗非鱼生长性能,促进其脂肪代谢和提高鱼体抗氧化能力有良好效果。基于L-肉碱对罗非鱼增重率和特定生长率的影响,推荐L-肉碱在吉富罗非鱼饲料中的添加量为150 mg/kg。     

不同投喂率和投喂频率对大杂交鲟幼鱼生长、体成分和生化指标的影响

为探讨大杂交鲟(Huso dauricus♀×Acipenser schrenckii♂)适宜投喂率和投喂频率,本实验分别设计了5个投喂率(0.4%、0.8%、1.2%、1.6%和2.0%)和5个投喂频率(1次/d、2次/d、3次/d、4次/d和5次/d),研究不同投喂率和投喂频率对大杂交鲟生长、体成分和生化指标的影响。投喂率实验中鱼初重(335.87±0.82)g,投喂频率实验中鱼初重(334.77±1.06)g,养殖周期为10周。结果表明,随着投喂率升高,实验鱼增重率、特定生长率、肝体比、脏体比、肥满度,肌肉粗蛋白、粗脂肪和肝粗脂肪含量显著升高(P0.05),血清谷丙转氨酶、谷草转氨酶和胃蛋白酶活性均显著升高(P0.05);饲料效率、全鱼和肌肉水分含量均显著降低(P0.05);全鱼粗脂肪含量,血清总蛋白、白蛋白和高密度脂蛋白胆固醇含量,肠脂肪酶活性呈先升高后降低趋势(P0.05)。随着投喂频率增加,实验鱼增重率、特定生长率和饲料效率无显著差异(P0.05);1次/d投喂频率组脏体比、肥满度和全鱼粗脂肪含量显著低于其他各组(P0.05),2次/d投喂频率组全鱼粗蛋白含量显著高于其他各组(P0.05)。不同投喂频率对实验鱼除血清葡萄糖含量以外的其他血清生化指标和胃肠消化酶活性或含量均无显著影响(P0.05)。综合以上结果认为,在300～600g大杂交鲟的养殖过程中日投喂率在1.2%～1.6%,投喂频率为2次/d比较适宜。     

大黄鱼幼鱼对饲料中锌需要量

以初始体重为(1.78±0.02)g的大黄鱼为实验对象,在室内流水系统(养殖桶规格:200L)中进行为期8周的摄食生长实验,研究大黄鱼对饲料中锌的需要量.通过在基础饲料中添加ZnSO4·H2O使饲料中锌含量分别达到9.68、30.63、48.94、91.28、167.49和326.81mg·kg-1.每种饲料设3个重复,每个重复放养40尾大黄鱼.实验采取饱食投喂方式,每天投喂2次(05:30和17:30),实验期间水温为26.5～29.5℃,盐度为25～28,溶解氧含量在7mg·L-1左右.实验结果表明各饲料处理组成活率(84.2%～96.7%)无显著差异.随着饲料中锌含量的增加,大黄鱼的特定生长率(SGR)显著升高[(2.47～2.77)%·d-1,P<0.05],且在91.28mg·kg-1锌饲料组达最大值(2.77%·d-1),然而,随着饲料中锌含量的进一步增加,SGR维持在一相对稳定水平,各处理组间体蛋白(14.0%～15.0%),体脂肪(5.4%～6.1%),灰分(3.7%～4.1%)及水分含量(76.1%～77.9%)均无显著差异(P0.05).饲料锌含量显著影响大黄鱼脊椎骨、全鱼和血清中锌的含量,而对肝脏锌含量无显著影响.以SGR与骨骼锌含量为评价指标,根据折线模型得出大黄鱼对饲料中锌的需要量分别为59.6和84.6mg·kg-1.     

饲料脂肪水平对许氏平鲉脂肪沉积、血液生化指标及脂肪代谢酶活性的影响

以鱼油为脂肪源,分别配制脂肪水平为3.7%、6.8%、9.6%、13.1%、15.6%的5种实验饲料,对平均初始体质量为(7.13±0.03)g的许氏平鲉进行为期60 d的饲养实验,探讨饲料脂肪水平对许氏平鲉形体指数、脂肪沉积、血液生化指标与脂肪代谢酶活性的影响。结果表明:肝体指数、脏体指数随着饲料脂肪水平的升高显著提高(P0.05),脂肪水平对肥满度没有显著影响(P0.05);许氏平鲉鱼体脂肪沉积随饲料脂肪水平的增加显著提高(P0.05),15.6%全鱼、肌肉、肝脏脂肪含量最高,显著高于3.7%、6.8%组(P0.05)。随着脂肪添加量的增加,许氏平鲉肝脏葡萄糖-6-磷酸脱氢酶(G6PDH)和苹果酸脱氢酶(MHD)活性显著降低(P0.05),15.6%与13.1%组G6PDH、MHD活性显著低于3.7%和6.8%组(P0.05);肝酯酶(HL)和脂蛋白酯酶(LPL)活性显著升高(P0.05),15.6%与13.1%组HL和LPL活性显著高于3.7%和6.8%组(P0.05)。血液甘油三酯(TG)和总胆固醇(CHO)含量随着饲料脂肪水平增加有下降的趋势,15.6%组的TG和CHO含量显著低于3.7%和6.8%组(P0.05);血液中高密度脂蛋白胆固醇(HDLC)、谷草转氨酶(AST)、谷丙转氨酶(ALT)与碱性磷酸酶(ALP)活性呈上升趋势(P0.05),15.6%组最高;低密度脂蛋白胆固醇(LDLC)呈先上升后下降的趋势(P0.05)。研究表明,饲料脂肪水平对许氏平鲉形体指数、脂肪沉积、血液生化指标及脂肪代谢酶活性影响显著,但过高的脂肪水平将使许氏平鲉肝脏脂肪沉积增多,当饲料脂肪水平高于9.6%时不利于鱼类健康生长。     

饲料蛋白质和脂肪水平对牛蛙生长性能的影响

为研究饲料中不同蛋白质和脂肪水平对牛蛙生长、体组成和肝脏健康的影响,以红鱼粉、豆粕和酪蛋白为蛋白源,鱼油和豆油为主要脂肪源,α-淀粉为主要糖源,微晶纤维素为填充剂,并补充无机盐和维生素等配制实验饲料。实验设3个蛋白水平(35%、40%和45%),每个蛋白水平下设4个脂肪水平(4%、7%、10%和13%),共12种饲料,饲料可利用能变化范围为12.4~17.8 kJ/g,蛋白能量比变化范围为21.9~32.0 mg/kJ。每种饲料设置3个重复,每个水族缸放养12只牛蛙[初始平均体质量为(91.5±1.1)g],每日饱食投喂2次,实验周期56 d。结果发现,饲料蛋白质和脂肪水平对牛蛙的存活率无显著影响,而13%脂肪组的牛蛙肝脏出现颜色不均一和肝体脆化无韧性的现象。饲料蛋白质和脂肪水平显著影响牛蛙的增重率、特定生长率、摄食率、饲料效率和蛋白质效率。其中,40%蛋白组牛蛙的增重率和特定生长率显著高于35%蛋白组,与45%蛋白组无显著差异。随着蛋白质水平的升高,饲料效率显著升高,而摄食率和蛋白质效率显著降低。随着脂肪水平的升高,增重率、特定生长率和摄食率显著升高,饲料效率、蛋白质效率和氮保留率无显著差异。饲料脂肪水平与牛蛙全体的脂肪含量和总能水平正相关,但不影响牛蛙全体的蛋白质含量。随着饲料脂肪水平的升高,牛蛙肝脏丙二醛含量显著升高,过氧化氢酶和脂蛋白酯酶活力先升高后降低。研究表明,牛蛙饲料适宜的蛋白质和脂肪水平分别为40%和7%,适宜蛋白能量比为27.7 mg/kJ。     

Effect of dietary carbohydrate level on growth performance,body composition,apparent digestibility coefficient and digestive enzyme activities of juvenile cobia,Rachycentron canadum L

A 9‐week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition and apparent digestibility coefficient and digestive enzyme activities of juvenile cobia. Six isonitrogenous and isolipidic diets containing graded levels of starch (1.3%, 6.5%, 12.5%, 18.4%, 24.2% and 30.4%) were fed to juvenile cobia. Specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary starch up to 18.4% (P<0.05), and thereafter SGR declined but FER and PER remained nearly the same. Apparent digestibility coefficient of starch reduced significantly when dietary starch up to 30.4%. Fish fed the diets with starch from 18.4% to 30.4% showed higher amylase activities in intestinal tract than those fed diets containing starch 1.3% and 6.5% (P<0.05). Significantly higher whole‐body lipid contents were observed in fish fed the diets containing higher starch. Whole‐body moisture content was inversely correlated with whole‐body lipid content, while protein and ash showed no significant differences. Plasma glucose, hepatosomatic index, liver glycogen and liver lipid increased with an increasing dietary starch. Based on SGR and FER, the appropriate dietary starch supplementations of juvenile cobia were estimated to be 21.1% and 18.0 % of diet respectively.     

Effects of Dietary Energy Level and Number of Meals on Growth and Body Composition of Nile Tilapia Oreochromis niloticus (L.) During Summer and Winter Seasons

Two feeding trials (experiments 1 and 2) were conducted to determine the combined effect of dietary energy levels (low energy, LE and high energy, HE) and number of daily meals (one meal with the entire daily amount, two meals with half of the daily amount, and three meals with one‐third of the daily amount) on the growth and body composition of Nile tilapia Oreochromis niloticus in a recirculating system at different water temperatures, representing winter and summer seasons. In experiment 1 (winter), weight gain and specific growth rate (SGR) were significantly (P < 0.05) affected by dietary energy levels, but not by number of meals. Weight gain and SGR for fish fed the LE diet one daily meal were significantly (P < 0.05) higher than for fish fed the HE diet in one daily meal. Feed efficiency ratio (FER) and energy efficiency ratio (EER) were significantly (P < 0.05) affected by dietary energy levels, but not by number of meals. Protein efficiency ratio (PER) was not significantly (P > 0.05) affected by either dietary energy levels or number of meals. However, protein retention was significantly (P < 0.05) affected by both dietary energy levels and number of meals. The chemical composition (moisture, protein, lipid, and ash) of fish muscle was not significantly (P > 0.05) affected by either dietary energy levels or number of meals. However, visceral fat content was significantly (P < 0.05) affected by dietary energy levels, but not by number of meals. In experiment 2 (summer), weight gain and SGR were significantly (P < 0.05) affected by number of meals, but not by dietary energy levels. Weight gain and SGR for fish fed the LE and HE diets in two daily meals were significantly (P < 0.05) higher than those fed one daily meal. FER and PER were significantly (P < 0.05) affected by number of meals, but not by dietary energy levels. The highest FER and PER were observed in fish fed two daily meals. EER was significantly (P < 0.05) affected by both dietary energy levels and number of meals. Moisture and protein content of the whole fish were not significantly (P > 0.05) affected by either dietary energy levels or number of meals. Lipid content was significantly (P < 0.05) affected by dietary energy levels, but not by number of meals. Based on the results of these experiments, Nile tilapia should not be fed high‐energy diets to improve fish performance even under a limited feed allowance during winter or summer. Fish grew rapidly when fed two daily meals during summer, but number of meals had no effect on fish performance during winter.     

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。     

Effect of dietary lipid level on growth performance,feed utilization and body composition of grouper <Emphasis Type="Italic">Epinephelus coioides</Emphasis> juveniles fed isonitrogenous diets in floating netcages

An experiment was conducted to determine the effect of dietary lipid levels on growth performance and body composition of grouper Epinephelus coioides juveniles cultured in floating netcages (1.5 m × 1 m × 1.5 m). Six isonitrogenous diets (53% dietary protein) with increasing dietary lipid concentration (5.16, 7.38, 9.73, 12.36, 14.13, 16.04% of dry material, DM) were fed to satiation to triplicate groups of 20 fish (mean weight: 10.9 ± 0.1 g) for 56 days. Dietary energy levels were 300, 322, 340, 371, 382, 400 kcal/100 g DM, respectively. Fish fed the 9L diet had the highest weight gain (WG) and specific growth rate (SGR), but they were not significantly different from that of fish fed the 7L or 12L diet (p > 0.05). FI varied inversely with dietary lipid levels. The poorest FCR and the lowest PER were observed in fish fed the 5L diet but these parameters showed no significant differences (p > 0.05) for fish fed the dietary lipid level ranging from 9 to 16%. Nitrogen intake decreased with dietary lipid levels. Fish fed the 7L diet showed the highest N gain, which was not markedly different from that of fish fed the 9L and 12L diets (p > 0.05). N retention was significantly lower in fish fed the 5L diet than in the other groups. Lipid intake and lipid gain increased with dietary lipid levels. Lipid retention (%) of the 7L diet was lowest but showed no significant differences among other treatments (p > 0.05). Proximate composition of fish body was significantly affected by dietary lipid level (p < 0.05). Body lipid content increased in direct proportion to dietary lipid levels. In contrast, moisture content of whole-body was correlated negatively to dietary lipid level. Dietary lipid content had no significant effect on protein content in whole-body and white muscle (p > 0.05). Condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) increased with increasing dietary lipid level. Based on second-order polynomial regression analysis of WG against dietary lipid level, a breakpoint of 10.0% was indicated to be the optimal dietary lipid concentration for maximum growth for grouper Epinephelus coioides juveniles cultured in floating netcages.     

Effect of Dietary Lipid Level and Feeding Frequency on the Growth,Feed Utilization,and Body Composition of Juvenile Spotted Seabass,Lateolabrax maculatus

A 6‐wk feeding trial was conducted to evaluate the effects of different dietary lipid levels and feeding frequencies on the growth performance, feed utilization, and body composition of juvenile spotted seabass, Lateolabrax maculatus. Two experimental diets were prepared with two different dietary lipid contents, low lipid (7%; LL) and high lipid (14%; HL). Each diet was fed to triplicate groups of fish (5.5 ± 0.01 g) to apparent satiation at three meals per day, two meals per day, one meal per day, and one meal every 2 d, respectively, for 6 wk. Fish growth performance in terms of weight gain (WG) and specific growth rate (SGR) was significantly affected by frequency of feeding, with increasing values as feeding frequency increased up to twice daily, regardless of dietary lipid content. In addition, fish fed the diet with the HL level (14%) showed significantly higher WG and SGR than those fed the LL diet (7%) at all the feeding frequencies tested. Feed efficiency (FE) and protein efficiency ratio (PER) were affected by both dietary lipid level and feeding frequency. FE and PER values were significantly higher in fish fed the HL diet and/or when fish were fed twice or thrice a day. However, daily feed intake and daily energy intake were significantly affected only by feeding frequency and were significantly reduced when the fish were fed only once every 2 d compared with those fed more frequently. Whole‐body moisture content of fish tended to decrease with increasing dietary lipid level and frequency of feeding. In contrast, whole‐body lipid content increased in fish as dietary lipid level and feeding frequency increased. Consequently, we can conclude that feeding spotted seabass twice daily to apparent satiation is acceptable and sufficient to achieve good growth and FE, as fish performance was not significantly enhanced when feeding was increased from two to three times daily.     

Use of a Compound Protein Source as a Replacement for Fish Meal in Diets of Large Yellow Croaker, Pseudosciaena crocea R.

A feeding trial was conducted to evaluate the potential of a compound protein source (CPS) as a replacement of fish meal (FM) in diets for large yellow croaker, Pseudosciaena crocea R. The CPS was made of soybean meal, meat and bone meal, peanut meal, and rapeseed meal (4:3:2:1 in weight) by adding crystalline l ‐methionine (0.77%), l ‐lysine (0.95%), and l ‐isoleucine (0.44%) to ensure the essential amino acid (EAA) contents of CPS diets to reach or exceed those of FM diet. Six isonitrogenous and isoenergetic diets (Diets 1–6) were formulated to contain 0, 9, 18, 27, 36, and 45% CPS replacing 0, 13, 26, 39, 52, and 65% FM protein, respectively. Triplicate groups of 180 fish (initial average 1.88 ± 0.01 g) were fed diets to apparent satiation by hand twice daily for 8 wk in floating sea cages (1.0 × 1.0 × 1.5 m). The water temperature ranged from 26.5 to 29.5 C, the salinity from 25 to 28‰, and the dissolved oxygen content was approximately 7 mg/L during the experimental period. The results showed that specific growth rate (SGR) and feed efficiency ratio (FER) of fish fed Diets 2 and 3 were not significantly different from those of fish fed control diet (Diet 1). However, SGR and FER of fish fed Diets 4–6 were significantly lower compared with control group (P < 0.05). The whole‐body proximate analysis showed that protein significantly decreased with increasing dietary CPS levels (P < 0.05), while the whole‐body lipid, ash, and moisture showed no significant differences among dietary treatments. Methionine, cystine, and lysine contents of the whole body were significantly influenced by dietary CPS level (P < 0.05), while other EAA contents showed no significant differences. Results of the present study indicated that CPS could replace about 26% FM protein in diets for the large yellow croaker on crude protein basis without adverse effect on growth.     

Influence of dietary lipid/protein ratio on survival,growth, body indices and digestive lipase activity in Snakehead (Channa striatus,Bloch 1793) fry reared in re‐circulating water system

Nine isoenergetic (18.5 kJ g^?1) diets were formulated in a 3 × 3 factorial design to contain three protein levels (350, 400 and 450 g kg^?1) for each of three lipid levels (65, 90 and 115 g kg^?1), respectively, and fed twice daily for 8 weeks to fish of mean initial weight 3.34 ± 0.02 g reared in a re‐circulatory water system. Temperature, pH and dissolved oxygen (DO) were maintained within the range 28–30 °C, 5.6–6.8 and 4.82–6.65 mg L^?1 respectively throughout. Results show that fish survival was better in the groups fed 65 g kg^?1 lipid while growth performance (% weight gain, WG; specific growth rate, SGR) and nutrient utilization (feed conversion ratio, FCR; protein efficiency ratio, PER; protein intake, PI) in the 65/450 and 90/450 g kg^?1 treatments were similar and significantly (P < 0.05) higher than in fish fed the other lipid/protein ratio combinations. The body indices monitored (Hepatosomatic index, HSI and viscerosomatic index, VSI) were similar among the treatments whereas intestinal lipase activity was not significantly (P < 0.05) affected by increase in dietary lipid and protein levels. Carcass composition showed that dietary protein level affected body protein content positively in the 65 and 90 g kg^?1 lipid treatments, but dietary lipid level did not affect body lipid content. A lipid/protein ratio of 65/450 g kg^?1 is considered adequate for good growth performance and survival of Channa striatus fry.     

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.