n-3高不饱和脂肪酸对黑鲷幼鱼生长及脂肪代谢的影响

研究了饲料中不同水平n-3 HUFA(0.79%,0.83%,0.85%,0.88%,0.92%,0.94%;DHA/EPA=2.8/1)对黑鲷幼鱼生长及脂肪代谢的影响.结果显示:(1)黑鲷幼鱼肝体指数(HSI)及腹脂率(IPF ratio)随饲料中n-3 HUFA含量的增加而减小,且于0.92%和0.94%组时显著低于其他各组;脂肪细胞直径呈减小趋势,其中0.94%组显著小于0.85%组;肌肉脂肪含量受n-3 HUFA的影响显著,于0.88%组时达到最低.各组全鱼水份和脂肪含量差异不显著(P＞0.05).肝脏、肌肉及腹腔脂肪组织饱和脂肪酸(∑SFA)和C16:0含量均随饲料n-3HUFA水平增加呈下降趋势,而∑n-3 HUFA呈显著上升趋势.各组织中DHA/EPA不受饲料脂肪酸组成的影响.以增重率为参考指标,二次回归分析结果表明,黑鲷幼鱼[(8.08±0.09)g]获得最佳增重时对饲料中n-3 HUFA的需要量为0.87%DM;(2)黑鲷幼鱼肝脏脂肪酸合成酶(FAS)活性及基因表达水平均在n-3 HUFA＞0.92%时有显著下降(P＜0.05);腹腔脂肪激素敏感脂肪酶(HSL)活性及基因表达水平均随饲料中n-3 HUFA的添加呈升高趋势(P＜0.05),且高含量n-3 HUFA(0.94%)可使HSL活性增加近一倍.结果表明,饲料中n-3HUFA通过同步调控脂肪合成与分解两个过程影响黑鲷幼鱼脂肪代谢.     

野生与人工养殖牙鲆亲鱼不同组织脂肪酸的比较

为研究脂肪酸对牙鲆繁育性能的影响, 采用生物化学方法, 对野生和养殖牙鲆亲鱼肌肉、肝脏及卵中脂肪酸组成分别进行测定。结果表明: (1) 牙鲆肌肉、肝脏和卵中脂肪含量大小关系为肝脏>卵>肌肉。野生亲鱼肌肉和卵中脂肪含量显著低于养殖亲鱼(P<0.05), 肝脏脂肪含量与养殖亲鱼无显著差异; (2) 牙鲆亲鱼3种组织中均检测出21种脂肪酸。野生亲鱼肌肉中饱和脂肪酸(SFA)与养殖亲鱼无显著差异, 单不饱和脂肪酸(MUFA)显著低于养殖亲鱼(P<0.05)。肝脏和卵中SFA显著高于养殖亲鱼(P<0.05), MUFA与养殖亲鱼无显著差异; (3) 野生亲鱼肌肉、肝脏和卵中高不饱和脂肪酸(PUFA)的含量, 尤其是肝脏和卵中C20:5n-3(EPA)、C22:6n-3(DHA)的含量均显著低于养殖亲鱼(P<0.05), 但肌肉和卵中的C20:4n-6(ARA)含量明显高于养殖亲鱼(P<0.05); (4) 野生牙鲆亲鱼肌肉、肝脏和卵中n-3/n-6 PUFA及EPA/ARA显著低于养殖亲鱼(P<0.05), 肝脏中DHA/EPA显著高于养殖亲鱼(P<0.05), 但野生亲鱼肌肉和卵中的DHA/EPA与养殖亲鱼无显著差异。比较结果说明, DHA、EPA和ARA等PUFA是与牙鲆繁殖性能密切相关的重要脂肪酸。在牙鲆亲鱼养殖过程中, 除了提供牙鲆亲鱼足够的脂肪酸营养外, 也应注意各种脂肪酸, 尤其是PUFA中各种脂肪酸之间的添加比例, 从而保证亲鱼的繁殖性能及卵和仔鱼的质量。     

n-3/n-6 HUFA对许氏平鲉幼鱼生长、体组成及组织脂肪酸组成的影响

为研究饲料n-3/n-6高不饱和脂肪酸(HUFA)对许氏平鲉幼鱼生长、体组成及组织脂肪酸组成的影响,配制了6种n-3/n-6 HUFA(D1:14.28,D2:9.26,D3:5.66,D4:3.06,D5:2.02,D6:1.50)的等氮等脂的实验饲料。以许氏平鲉幼鱼(36.30±0.03) g为研究对象,在网箱中养殖65 d,分为6实验组,每组设3个重复,每个重复30尾鱼。结果发现:①饲料n-3/n-6 HUFA对许氏平鲉幼鱼的成活率无显著影响。随着n-3/n-6 HUFA降低,幼鱼增重率呈先上升后下降趋势,饲料系数呈相反趋势,D2和D3组的增重率显著高于各组。②全鱼和肌肉粗脂肪含量呈先上升后下降趋势,分别在D2、D3组达到最大值。肝脏粗脂肪含量呈先下降后上升趋势,D2组显著小于其他各组。③各组织C20:4n-6含量随n-3/n-6 HUFA的降低均呈上升趋势,而C20:5n-3、C22:6n-3和n-3/n-6 HUFA整体呈下降趋势。④鱼体脂肪酸组成受饲料影响程度由大到小依次为腹脂、肌肉、全鱼、肝脏,且各组织C20:5n-3与饲料C20:4n-6均呈显著负相关。研究表明,在本实验条件下,饲料中适宜比例(5.66～9.26)的n-3/n-6 HUFA显著提高实验鱼的生长,改变体组成及组织脂肪酸组成,以增重率和饲料系数作评价指标,经一元二次回归分析得许氏平鲉幼鱼饲料中n-3/n-6 HUFA的适宜比例分别是8.93和8.70。     

闽东海域银鲳亲鱼性腺发育后期脂类及脂肪酸蓄积特点

脂肪和脂肪酸是海水鱼类早期生长发育的重要结构物质和能量来源。亲鱼的脂肪和脂肪酸储备影响其繁殖性能和早期仔鱼的发育。为了获知银鲳亲鱼性腺发育后期脂类及脂肪酸蓄积特点,本研究采用氯仿甲醇法及气相色谱法定量检测了繁殖季节闽东海域野生银鲳亲鱼不同组织的总脂肪及脂肪酸含量。结果表明:亲鱼卵巢、精巢、肝脏和肌肉的总脂肪含量差异显著。卵巢、精巢、肝脏和肌肉的总脂含量分别为:35.76%,15.11%,22.07%和22.14%(占组织干重)。极性脂肪占总脂肪的比例在精巢中最高,其次为肝脏和卵巢,在肌肉中最低。性腺从Ⅳ期发育到Ⅴ期,雌鱼卵巢总脂肪和中性脂肪含量显著增加,雄鱼肌肉极性脂肪含量显著降低。中性脂肪中卵巢的20∶5n-3(EPA,2.25~3.87 mg/g)、22∶6n-3(DHA,6.71~13.03mg/g)和高不饱和脂肪酸(HUFAs,17.20~29.64 mg/g)含量最高,极性脂肪中精巢的EPA(0.38~0.27 mg/g)和DHA(3.12~3.59 mg/g)含量最高。性腺中n-3/n-6比值显著高于肝脏和肌肉中。随着卵巢发育,DHA等必需脂肪酸在雌鱼不同组织及同一组织不同脂肪类别之间存在转移现象。研究表明,银鲳亲鱼各组织的总脂肪含量、总脂肪组成及脂肪酸绝对含量(mg/g干物质)具有组织特异性,随着性腺发育,必需脂肪酸总体上表现为由肌肉和肝脏向性腺中转移,且性腺中脂肪酸的变化主要发生在中性脂肪中。     

不同脂肪源对真鲷幼鱼生长、存活及体内脂肪酸组成的影响

真鲷幼鱼摄食缺乏多不饱和脂肪酸(PUFA)饵料时,其生长增重率和存活率比摄食富含PUFA配合饵料或玉筋鱼鱼糜的明显下降。幼鱼摄食含有不同脂肪酸饵料时,其肌肉和肝脏组极性或非极性脂中脂肪酸组成都有变化。肌肉和肝脏极性脂中的PUFA比非极性脂中PUFA含量高,并且当饵料中不能提供足够的PUFA时,非极性脂中的PUFA下降明显,而极性脂中的PUFA变化较小,被优先贮存。真鲷幼鱼肌肉和肝脏组织缺乏n-9、n-6和n-3相互转化的能力。因此,为提高幼鱼的生长增重率和存活率,必须保证饵料中含有足够的PUFA。     

细鳞鲑幼鱼n-3 HUFA需求量的研究

为确定细鳞鲑(Brachymystax lenok)n-3 HUFA需求量以减少鱼油使用和降低养殖成本,研究饲料中不同水平的n-3 HUFA对细鳞鲑的生长性能、体成分和肌肉脂肪酸组成的影响。以脱脂鱼粉、脱脂豆粕、明胶和酪蛋白为主要蛋白源,通过调节饲料中的猪油和浓缩油EPA、DHA水平,使饲料n-3HUFA的含量分别达到0.25%、0.50%、0.75%、1.00%、1.25%、1.50%,配制出6种等氮等能的试验饲料(D 0.25、D 0.50、D 0.75、D1.00、D 1.25和D 1.50),分别投喂细鳞鲑幼鱼(60.0 g±2.8 g)84 d。结果显示:饲料中n-3HUFA不同水平对细鳞鲑成活率和饲料系数没有显著影响,但是显著影响了其末重(FW)、增重率(WGR)和特定生长率(SGR)。随着添加饲料中n-3HUFA水平的升高,FW、WGR和SGR有先升高后下降的趋势,且3者在饲料中n-3HUFA水平为0.75%均最大。随着饲料中n-3 HUFA水平的升高,鱼肌肉18∶1n-9的含量逐渐下降,而22∶6n-3的水平相应升高。结果表明,以WGR为评价指标时,用二次曲线模型推测出细鳞鲑对饲料n-3 HUFA的需求量约为0.69%。     

不同脂肪酸含量及比例对黄颡鱼幼体组成影响的研究

在粗蛋白42%和粗脂肪8%的半精制饵料中,添加不同剂量的鱼油、玉米油、花生油和芝麻油,使20C:5n-3(EPA)+22C:6n-3(DHA)的含量(占总脂肪的%)和n-3/n-6比例分别为14.942,0.728;15.551,0.851;19.365,1.238;19.976,1.345和20.457,1.406。饲喂黄颡鱼(Pelteobagrus fulvidraco,Richardson)幼鱼50 d,研究了不同脂肪酸含量及比例对黄颡鱼幼鱼体组成的影响。结果表明,随着饵料中EPA+DHA的含量和n-3/n-6比例的逐渐增加,鱼体肌肉中水分含量逐渐增加,粗蛋白含量逐渐降低,肌肉中的n-3脂肪酸含量和n-3/n-6比例逐渐增加,肌肉的n-6和n-9脂肪酸含量逐渐降低。     

微粒饲料中以微藻粉替代鱼油对牙鲆(Paralichthys olivaceus)稚鱼生长存活和脂肪酸组成的影响

以18日龄的牙鲆(Paralichthys olivaceus)稚鱼为研究对象,通过11 d的生长实验,研究了添加不同比例的微藻粉替代鱼油对牙鲆稚鱼生长、存活率和脂肪酸组成的影响。以鱼油组(FO)为对照组,以裂壶藻粉(Schizochytrium sp.)、微绿球藻粉(Nannochloropsis sp.)和橄榄油替代不同比例的鱼油,配制成5组等氮等能的实验饲料,分别命名为鱼油组(FO),50%混合替代组(M50)、100%混合替代组(M100)、100%裂壶藻橄榄油替代组(S100)、100%微绿球藻橄榄油替代组(N100)。结果显示,微藻粉替代鱼油对牙鲆稚鱼的生长无显著影响;含有裂壶藻的各饲料组(M50、M100、S100)成活率显著高于FO组和N100组(P?0.05);微藻粉替代鱼油不影响牙鲆稚鱼主要脂肪酸的组成;Person相关性分析发现,C14:0、C16:1n-7、C18:2n-6、C20:0、C18:3n-3、C22:0、C20:4n-3、EPA、C22:5n-6和DHA的百分含量均与其饲料中的百分含量呈显著正相关(P0.05);总饱和脂肪酸、总单不饱和脂肪酸、n-3多不饱和脂肪酸的百分含量以及DHA/EPA比率均与其饲料组成表现出显著正相关(P0.05)。综上所述,微藻作为脂肪源替代鱼油完全可以满足牙鲆稚鱼的生长和发育,各种脂肪酸均可以被牙鲆稚鱼充分消化和吸收,并且添加两种微藻后提高了稚鱼的DHA含量和DHA/EPA比率,与鱼油对照组相比显著提高了牙鲆稚鱼的成活率。因此,以微藻替代鱼油在牙鲆稚鱼的培育中是可行的。     

n-3/n-6 HUFA对大菱鲆幼鱼生长性能、全鱼脂肪酸组成和血清生化指标的影响

为探讨饲料中不同n-3/n-6高不饱和脂肪酸(HUFA)对大菱鲆幼鱼生长性能、全鱼脂肪酸组成和血液生化指标的影响,配制了6种不同n-3/n-6 HUFA(D1:29.54,D2:23.04,D3:18.97,D4:9.06,D5:6.86,D6:3.87)的实验饲料。以大菱鲆幼鱼(12.18±0.01)g为研究对象,在循环水养殖系统中开展了为期8周的养殖实验。实验共分6组,每组3个重复,每个重复35尾鱼。结果显示:饲料中n-3/n-6 HUFA对大菱鲆幼鱼的成活率(SR)无显著影响;增重率(WGR)、特定生长率(SGR)和蛋白质效率(PER)呈先上升后下降趋势且D6组的显著低于其他各组,D2组蛋白质效率显著高于其他各组。全鱼粗蛋白和灰分均呈先上升后下降趋势;D6组肌肉粗蛋白和灰分显著低于其他各组。全鱼ARA含量随着n-3/n-6 HUFA的下降呈上升趋势;全鱼中EPA、DHA、n-3/n-6多不饱和脂肪酸(PUFA)和n-3/n-6 HUFA均随着饲料中n-3/n-6 HUFA的下降呈下降趋势。血清中酸性磷酸酶(ACP)和超氧化物歧化酶(SOD)随着n-3/n-6 HUFA的变化呈上升趋势;溶菌酶(LZM)和总抗氧化能力(T-AOC)呈先上升后下降的趋势,溶菌酶在D2组达到最大值,总抗氧化能力在D3组达到最大值。综上所述,饲料中n-3/n-6 HUFA在适宜范围(18.97~23.04)显著提高了实验鱼的生长性能和非特异性免疫力,改变了鱼体组织的常规成分和脂肪酸组成。     

黄海海域5种底栖型海水鱼类组织脂肪酸组成特征分析

本研究测定和评估了青岛地区5种底栖型海水鱼[(黄鮟鱇(Lophius litulon)、鲬(Platycephalus indicus)、长绵鳚(Zoarces viviparu)、角木叶鲽(Pleuronichthys cornutus)和带纹条鳎(Zebrias zebrinus)]的形体指标、肌肉和肝脏的粗成分,以及肌肉、肝脏、脑、眼、皮肤、肠道等组织的脂肪酸组成,以全面评估底栖型代表鱼类的脂肪和脂肪酸组成特征。实验鱼每种鱼9尾,3尾一组混样作为一个重复。结果显示,在5种鱼中,肌肉脂肪含量整体偏低,黄鮟鱇和带纹条鳎肌肉脂肪含量尤其低(0.3%~0.4%),但黄鮟鱇、鲬和角木叶鲽具有较高的肝脏脂肪含量(19%~29%),而带纹条鳎和长绵鳚肝脏脂肪含量偏低(4%~5%)。脂肪酸组成方面,黄鮟鱇肌肉中n-3系列长链多不饱和脂肪酸(long chain-polyunsaturated fatty acid, LC-PUFA)含量显著高于其他鱼,尤其以DHA最为明显。黄鮟鱇背肌中还具有最高含量的18:1n-9。长绵鳚背肌脂肪酸组成最明显的特征是较低的16:0含量和较高的20:4n-6及EPA含量。肝脏脂肪酸中,鲬和角木叶鲽具有显著高的18:1n-9等单不饱和脂肪酸含量,但其DHA含量较低。在黄鮟鱇、带纹条鳎和长绵鳚的大多组织中均有较高的DHA、20:4n-6和22:5n-3,但EPA含量较低。研究表明,即使同为底栖型鱼类,不同种类间脂肪和脂肪酸组成差异也非常显著。黄鮟鱇具有显著高的n-3 LC-PUFA含量,脂肪酸营养价值较高。     

Alteration of liver and muscle fatty acid composition in gilthead seabream (Sparus aurata) juveniles held at high stocking density and fed an essential fatty acid deficient diet

The aim of the present study was to determine the combined effect of both stress and EFA deficiency on several biological and biochemical parameters. Fish were fed during 15 weeks two isocaloric and isoproteic diets: a control diet based on fish oil and formulated to meet the n-3 HUFA requirements for this species (1.5% of n-3 HUFA) and a deficient diet containing beef tallow and formulated to be deficient in n-3 HUFA. Each experimental diet was evaluated both at high and low stocking densities (10 and 3.2 kg m^–3 of initial density, respectively).High stocking density produced a chronic stress situation with elevation of plasma cortisol levels. It also caused a reduction in hepatosomatic index and liver lipid contents, increasing the oleic acid/n-3 HUFA ratios in the polar lipids. Fish fed the EFA deficient diet at low stocking density showed common deficiency symptoms. High stocking density in fish fed the EFA deficient diet induced a higher degree of EFA deficiency symptoms leading to mortality, liver steatosis, liver lipid deposition, reduced muscle lipid and reduced n-3 HUFA contents, which particularly affected EPA, but not DHA, suggesting a preferential retention of the latter fatty acid, specially in the phosphoglycerides fraction.     

Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~ 0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9–10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon.     

Requirement of n-3 long chain polyunsaturated fatty acids for European sea bass (Dicentrarchus labrax) juveniles: growth and fatty acid composition

European sea bass juveniles (14.4±0.1 g mean weight) were fed diets containing different levels of fish oil then of n-3 highly unsaturated fatty acids (n-3 HUFA) for 12 weeks. The fish performance as well as fatty acid (FA) composition of neutral and polar lipids from whole body after 7 and 12 weeks feeding were studied. The requirements of juvenile sea bass for n-3 highly unsaturated fatty acids (n-3 HUFA) were studied by feeding fish diets containing six different levels of n-3 HUFA ranging from 0.2% to 1.9% of the diet, with approximately the same DHA/EPA ratio (1.5:1).

The growth rate at the end of the trial showed significant differences. Fish fed low dietary n-3 HUFA (0.2% DM of the diet) showed significantly lower growth than the diet 3 (0.7%), then no further improvement (P>0.05) of growth performance was seen by elevating the n-3 HUFA level in the diet up to 1.9% (diet 6). No difference in feed efficiency, protein efficiency ratio or protein retention was observed among treatments, nor in protein and total lipid content. However, the n-3 HUFA levels in diets highly influenced fish fatty acid composition in neutral lipid, while polar lipid composition was less affected. Comparison of polar lipid content after 7 or 12 weeks indicated that DHA remained stable at the requirement level, while arachidonic acid decreased with time. Results of this experiment suggest that the requirement for growth of n-3 HUFA of juvenile sea bass of 14 g weight is at least 0.7% of the dry diet.     

Essentiality of Dietary n-3 Highly Unsaturated Fatty Acids in Juvenile Japanese Flounder Paralichthys olivaceus

This study was conducted to confirm the essentiality of dietary n-3 highly unsaturated fatty acids (n-3 HUFA) and to investigate the effects of dietary lipid sources on growth performance, liver, and blood chemistry in juvenile Japanese flounder. Three replicate groups of fish (average weighing 3.0 g) were fed experimental diets containing lauric acid ethyl ester, soybean oil, soybean and linseed oils mixture, and squid liver oil as lipid sources for 13 wk. No significant difference was observed in survival among all groups ( P >0.05). Weight gain, feed efficiency and protein efficiency ratio of fish fed the squid liver oil diet containing high n-3 HUFA level were significantly higher than those of fish fed the other diets ( P 0.05). Saturated and monounsaturated fatty acids of liver polar and neutral lipid fractions in fish fed the diet containing lauric acid tended to increase compared to those of the other groups. Fish fed the diets containing soybean and/or linseed oils, which contained high contents of 18:2n-6 and 18:3n-3, respectively, showed the highest contents of 18:2n-6 and 18:3n-3 in both lipid fractions of the liver ( P 0.05). Significantly higher content of n-3 HUFA was observed in both lipid fractions of the liver from fish fed the diet containing squid liver oil than for fish fed the other diets ( P 0.05). Total cholesterol, glucose, and glutamic-oxaloacetic acid transaminase in plasma were significantly affected by dietary lipids ( P 0.05). Histologically, the liver of fish fed the diet containing squid liver oil had a clear distinction between nuclear and cytoplasm membranes; however, cytoplasm of fish fed the diets containing lauric acid and soybean oil was shrunken, and the hepatic cell outline was indistinguishable. It is concluded that the dietary n-3 HUFA is essential for normal growth, and that the dietary lipid sources affect growth performance, liver cell property, and blood chemistry in juvenile Japanese flounder.     

Lipid classes and fatty acids during embryogenesis of captive and wild silverside (<Emphasis Type="Italic">Chirostoma estor estor</Emphasis>) from Pátzcuaro Lake

Lipid classes and fatty acid levels were analyzed in freshly fertilized eggs, early and late embryo development, and freshly hatched larvae obtained from wild and captive silverside Chirostoma estor estor broodstock, as well as in plankton, Artemia, and pelleted feed. The concentration of triglycerides (TGs) and highly unsaturated fatty acids (HUFAs) in neutral lipid fraction significantly decreased during early development and especially after hatching, whereas phospholipids and HUFA in polar lipid fraction remained constant. These results indicate that TGs rather than PLs are used as energy sources and that all HUFAs [20:4n-6/arachidonic acid (ARA), 20:5n-3/eicosapentaenoic acid (EPA), and 22:6n-3/docosahexaenoic acid (DHA)] of polar lipids are selectively conserved during early development. High levels of DHA (30%, on average, of total fatty acids) and low levels of EPA (4%) were observed in eggs, embryos, and larvae and did not reflect the proportions of these fatty acids in food. Preferential accumulation of DHA from food consumed by broodstock, and then transference to eggs, was probably occurring. The main difference between eggs from both origins was a low level of ARA in eggs from captive fish (4% of total fatty acids) compared to wild fish (9%). This could be associated with a deficiency in the diet that is not compensated for by desaturation/elongation of 18:2n-6 and, possibly, with greater stress in captive fish. In any case, particular requirements of ARA should be determined to optimize the culture of C. estor.     

Body lipid and fatty acid composition in male gilthead seabream broodstock at different stages of the reproductive cycle: effects of a diet lacking n-3 and n-6 HUFA

Total lipid (TL), lipid classes and fatty acid composition of neutral (NL) and polar (PL) lipids were studied in the gonads, liver and muscle of gilthead seabream males ( Sparus aurata ) fed a control diet (diet C) or an n-3 and n-6 highly unsaturated fatty acids (HUFA)-deficient diet (diet D), at different stages of the reproductive cycle. Between pre-spermatogenesis (November) and spermatogenesis (March), the lipid content was high and particularly rich in cholesterol, phosphatidylcholine and phosphatidylethanolamine in gonads from both dietary groups. At post-spermatogenesis (June), TL and especially PL dramatically decreased in the gonads from both groups. However, at this period diet C fish gonads were richer in triacylglycerides (TAG) than those from diet D fish. The liver lipid contents and particularly TAG were over 200% lower in June than in March for both groups. Nevertheless, the most noteworthy depletion of lipids during this period was achieved by the n-3 HUFA in diet D fish. Conversely, arachidonic acid (20:4n-6) did not decrease in NL or PL from gonads and liver in groups C and D. Muscle lipids from diet C fish were relatively insensitive to seasonal influences. However, in June, the muscle TAG content was significantly reduced in diet D fish.     

Influence of broodstock gilthead seabream (Sparus aurata L.) dietary fatty acids on egg quality and egg fatty acid composition throughout the spawning season

The influence of broodstock dietary lipids on egg quality and egg fatty acid composition throughout the spawning season of gilthead seabream was investigated. For this purpose, the fish were fed for 7 months either a control diet (diet C) or a diet deficient in n−3 highly unsaturated fatty acids (n−3 HUFA) but rich in both oleic (18:1n−9) and linolenic (18:3n−3) acids (diet D). Eggs spawned by both groups of fish were sampled at the beginning, middle and end of the spawning season and the fatty acid composition of their neutral (NL) and polar lipids (PL) determined. In the early season, percentages of fertilized and hatched eggs, relative proportions of NL and PL as well as their fatty acid compositions, were not affected by the lipid composition of the broodstock diet. However, the eggs spawned during the middle and late seasons showed marked differences among the two groups of fish, clearly reflecting the influence of dietary fatty acids. This influence was more evident in the neutral lipid fraction than in the polar lipids. No correlation was found between the number of buoyant eggs and eicosapentaenoic (20:5n−3, EPA), docosahexaenoic (22:6n−3, DHA) fatty acids or total n−3 HUFA contents in egg phospholipids. However, a negative correlation was detected when percentages of fertilized eggs were compared with the levels of 18:1n−9, 18:3n−3 and with the ratio 18:1n−9/n−3 HUFA present in the phospholipids. Our results indicate the importance of maintaining not only the level of n−3 HUFA in egg membrane phospholipids, but also the balance between n−3 HUFA and other fatty acids such as 18:1n−9 and 18:3n−3, in order to obtain a high spawning quality.     

Essential fatty acid requirement of juvenile red drum (Sciaenops ocellatus)

Feeding experiments and laboratory analyses were conducted to establish the essential fatty acid (EFA) requirement of red drum (Sciaenops ocellatus). Juvenile red drum were maintained in aquaria containing brackish water (5 ± 2‰ total dissolved solids) for two 6-week experiments. Semipurified diets contained a total of 70% lipid consisting of different combinations of tristearin [predominantly 18:0] and the following fatty acid ethyl esters: oleate, linoleate, linolenate, and a mixture of highly unsaturated fatty acids (HUFA) containing approximately 60% eicosapentaenoate plus docosahexaenoate. EFA-deficient diets (containing only tristearin or oleate) rapidly reduced fish growth and feed efficiency, and increased mortality. Fin erosion and a “shock syndrome” also occurred in association with EFA deficiency. Of the diets containing fatty acid ethyl esters, those with 0.5–1% (n-3) HUFA (0.3–0.6% eicosapentaenoate plus docosahexaenoate) promoted the best growth, survival, and feed efficiency; however, the control diet containing 7% menhaden fish oil provided the best performance. Excess (n-3) HUFA suppressed fish weight gain; suppression became evident at 1.5% (n-3) HUFA, and was pronounced at 2.5%. Fatty acid compositions of whole-body, muscle and liver tissues from red drum fed the various diets generally reflected dietary fatty acids, but modifications of these patterns also were evident. Levels of saturated fatty acids appeared to be regulated independent of diet. In fish fed EFA-deficient diets (containing only tristearin or oleate), monoenes increased and (n-3) HUFA were preferentially conserved in polar lipid fractions. Eicosatrienoic acid [20:3(n-9)] was not elevated in EFA-deficient red drum, apparently due to their limited ability to transform fatty acids. Red drum exhibited some limited ability to elongate and desaturate linoleic acid [18:2(n-6)] and linolenic acid [18:3(n-3)]; however, metabolism of 18:3(n-3) did not generally result in increased tissue levels of (n-3) HUFA. Based on these responses, the red drum required approximately 0.5% (n-3) HUFA in the diet (approximately 7% of dietary lipid) for proper growth and health.     

Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

The desaturation and elongation of [1-¹⁴C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.     

Efficacy of dietary methyl esters of n−3 HUFA vs. triacylglycerols of n−3 HUFA by gilthead seabream (Sparus aurata L.) juveniles

A feeding experiment was carried out on gilthead seabream juveniles to investigate the utilization of dietary n−3 highly unsaturated fatty acids (n−3 HUFA), when presented as methyl esters or as triacylglycerols. Three groups of gilthead seabream juveniles, of an initial mean weight of 62 g, were fed diets containing the same level of n−3 HUFA (about 2% dry weight basis, DWB) but where these essential fatty acids (EFA) were supplied in the form of methyl esters, triacylglycerols or as a mixture of these two chemical forms (diets 1, 2 and 3, respectively). A fourth group of 62-g individuals was fed a diet containing a particularly high level of triacylglycerols of n−3 HUFA (about 5% DWB). After 8 weeks of feeding, the results showed that fish growth, hepatosomatic index, total lipid content, and fatty acid composition of neutral and polar lipids of brain, liver, gills and muscle were not affected by the chemical form of the lipids given in the diet. However, individuals fed the very high level of EFA (diet 4) showed a lower growth rate than the other three groups of fish. In addition, eicosapentaenoic acid (EPA; 20:5n−3) and docosahexaenoic acid (DHA; 22:6n−3) levels in both neutral and polar lipids from liver, gills and muscle were higher in this group of fish, with the brain fatty acid composition being less affected by dietary regime.