Influence of n-3 highly unsaturated fatty acid deficiency on the lipid composition of broodstock gilthead seabream (Sparus aurata L.) and on egg quality

A feeding experiment was conducted on gilthead seabream (Sparus aurata) broodstock to investigate the incidence of n-3 highly unsaturated fatty acids (n-3 HUFA) dietary deficiencies on the lipid composition of female liver, gonads and eggs, in relation to spawning quality. Broodstock were fed a control (C) diet or a n-3 HUFA deficient (D) but linolenic acid rich diet. After 20 weeks of feeding, the results showed that levels of total neutral (TNL) and total polar (TPL) lipids of female gonads and eggs were independent of diet. However the fatty acid composition of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI) of female liver, gonads and eggs in the two groups of fish showed marked differences, reflecting the influence of fatty acid levels in the broodstock diets. This influence was even higher in TNL than in the phospholipid classes examined. In fish fed n-3 HUFA deficient diet, fatty acid composition of TNL of female gonads and eggs reflected the diet more than liver. A higher egg production in broodstock fed C diet (1.8% n-3 HUFA in diet) was extended to spawning quality such as percentages of fertilised and hatched eggs.     

Effects of a diet lacking HUFA on lipid and fatty acid content of intestine and gills of male gilthead seabream (Sparus aurata L.) broodstock at different stages of the reproductive cycle

A feeding experiment was carried out to determine the effect of a diet lacking n-3 and n-6 highly unsaturated fatty acids (HUFA) on lipid and fatty acid content in intestine and gills of male gilthead seabream (Sparus aurata L.) broodstock at different stages of the reproductive cycle: November (pre-spermatogenesis), March (spermatogenesis), and June (post-spermatogenesis). For this purpose, gilthead seabream broodstock were fed either a control diet (C) or an n-3 and n-6 HUFA-deficient diet (D). The results showed no changes in fatty acid content of polar lipids of intestine and gills from fish fed diet C at different stages of the reproductive cycle. However, significant changes were observed in the fatty acid content of neutral lipids in intestine but not in gills in this group. Thus, between November and March, saturates and n-3 HUFA decreased while monoenes increased. In June, the contents of these fatty acids had returned to their initial values (November). Moreover, in fish fed diet D, the fatty acid content of neutral lipid changed in both intestine and gills. In intestine NL, a decrease in saturates and n-3 HUFA and an increment in monoenes were observed from November to June. In gills, a decrease was also observed in n-3 HUFA from NL along the cycle. Nevertheless, n-6 HUFA content remained unchanged. These results show both tissue specificity in seasonal mobilization of fatty acids linked to reproductive processes and the influence of dietary fatty acids on body composition.     

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.     

Comparison of dietary phospholipids and neutral lipids: effects on gut, liver and pancreas histology in Atlantic cod (Gadus morha L.) larvae

The aim of the present study was to compare effects of dietary n-3 highly unsaturated fatty acids (HUFA) being incorporated in the phospholipid (PL) or in the neutral lipid (NL) fraction of the larval feed, on larval growth and histology of digestive organs in Atlantic cod ( Gadus morhua L.) larvae. Three isoproteic and isolipidic diets, labelled according to the percentage of n-3 docosahexaenoic acid and eicosapentaenoic acid contained in NL1 or in PL1 and PL3 of the diets, were fed to cod larvae from 17 days post hatching (dph) to 45 dph.
In the liver, hepatocytes and their nuclei were smaller in NL1 larvae compared with the PL larvae; the mitochondrial membrane structures were less dense and the amount of lipids observed in the liver was significantly higher in NL1 larvae compared with the PL3 larvae. The liver and gut size was related to larval size, with no differences between the larval groups. The results demonstrated that the essential fatty acids were more beneficial for cod larvae when they were incorporated in the dietary polar PL rather than in the NL, and that the n-3 HUFA requirements in cod larvae is possibly higher than that in the PL1 diet.     

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.     

Essential fatty acids in Atlantic salmon: time course of changes in fatty acid composition of liver, blood and carcass induced by a diet deficient in n-3 and n-6 fatty acids

Atlantic salmon fry (4 g) were fed a semi-synthetic diet devoid of n-3 and n-6 polyunsaturated fatty acids (PUFA) for 4 months. External signs of nutritional imbalance during the period were slow growth rate and increased mortality. Some symptoms of essential fatty acid deficiency appeared in the fatty acid composition of the blood and liver during the fourth month. At that time, the percentages of n-3 and n-6 PUFA of triacylglycerols (TAG) were nearly exhausted, and the percentages of 22:6 n-3 and of 20:5 n-3 in phospholipids (PL) showed a marked decrease. This decrease in the PUFA level of the PL was paralleled by the appearance of 20:3 n-9, whereas in the TAG an increase in the percentage of 18:1 n-9 was observed. After 4 months the monounsaturated fatty acid 18:1 n-9 constituted nearly 50% of the fatty acids in the TAG fraction of the liver. The time course of the changes in fatty acid composition of liver and blood lipids was quite similar, whereas the carcass lipid composition appeared to respond slowly to a diet devoid of essential fatty acids.     

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.     

Incorporation of fatty acids from dietary neutral lipid in eye, brain and muscle of postlarval turbot fed diets with different types of phosphatidylcholine

Previous results demonstrated the stimulating effect of soybean phosphatidylcholine (PC) on the utilization of dietary neutral lipid in larval and postlarval fish. The present study further investigated the effect of the degree of saturation of dietary PC on the enhancement of dietary fatty acid incorporation in lipids of turbot. Newly-weaned turbot were fed for 20 days on four isolipidic diets containing the same amount of highly unsaturated fatty acids (HUFA), presented either as neutral lipid, i.e. fish oil ethyl esters, or as polar lipid. Diet FO was a phospholipid-free control diet. Diets HPC, SPC and FPC were supplemented with 3% hydrogenated soybean PC, 3% native soybean PC and 3% marine fish roe PC, respectively.The three PC-supplemented diets resulted in better growth and higher muscle triacylglycerol levels than the PC-free diet FO. The fish fatty acids were determined in 3 lipid classes (neutral lipid, PC, phosphatidylethanolamine) of 3 organs or tissues (eye, brain and muscle). Despite the identical amounts of n-6 and n-3 fatty acids provided by the soybean oil and by the HUFA ethyl esters, the substitution of 3% hydrogenated coconut oil in diet FO by 3% hydrogenated PC in diet HPC caused, averaged over the various tissues and lipid classes, a 7 to 12% higher incorporation of 18:2n-6, 20:4n-6, 20:5n-3 and a 32% higher 22:6n-3 level in turbot lipid. Diet HPC appeared as efficient as diet SPC for enhancing the incorporation of the n-3 HUFA from the ethyl esters. Feeding diet FPC, in which the n-3 HUFA were provided through the marine PC source, resulted in slightly higher levels of these fatty acids in the fish than feeding the ethyl ester HUFA diets, even if supplemented with PC. Present results confirm the positive effect of PC, either hydrogenated or native, on the utilization of fatty acids provided in the diet as neutral lipid. The slightly higher incorporation of HUFA, when esterified on dietary PC instead of neutral lipid, raises the question regarding the form of intestinal absorption of PL in fish.p>     

Influence of dietary polar lipids' quantity and quality on ingestion and assimilation of labelled fatty acids by larval gilthead seabream

Dietary supplementation of phospholipids seems to be extremely important to promote growth and survival in fish larvae. Several studies also suggest the importance of n-3 highly unsaturated fatty acids (HUFA) rich phospholipids to further enhance larval performance. In the present study, four different diets were formulated in order to compare the effect of total dietary polar lipid contents, of soya bean lecithin supplementation and of feeding n-3 HUFA in the form of neutral or polar lipids on ingestion and incorporation of labelled fatty acids in gilthead seabream larvae. These diets were prepared including radiolabelled fatty acids from palmitoyl phosphatidylcholine, glycerol trioleate, free oleic acid (FOA) and free eicosapentaenoic acid (FEPA) and were fed to 25 day-old larvae. The results of these experiments showed that the elevation of the dietary polar lipid levels significantly improved microdiet ingestion, regardless of the origins of the polar lipids. This effect caused an improved incorporation of phosphatidylcholine fatty acids to the larval polar and total lipids (TL) as the dietary polar lipids increased. Nevertheless, a better incorporation of fatty acids from dietary polar lipids in comparison with that of fatty acids from dietary triglycerides into larval lipids was found in gilthead seabream, whereas a better utilization of dietary triglycerides fatty acids than dietary free fatty acids could also be observed. Besides, the presence of n-3 HUFA rich neutral lipids (NL) significanlty increased the absorption efficiency of labelled oleic acid from dietary triglycerides, but the presence of n-3 HUFA rich polar lipids, particularly improved the incorporation of FEPA. This fatty acid was preferentially incorporated into larval polar lipids in comparison with FOA.     

Effects of dietary phospholipid and highly unsaturated fatty acid on the gonadal development, tissue proximate composition, lipid class and fatty acid composition of precocious Chinese mitten crab, Eriocheir sinensis

Precocious puberty is a major constraint to the economical rearing Eriocheir sinensis farming. Although dietary phospholipid (PL) and highly unsaturated fatty acids (HUFA) reportedly enhanced ovarian development in normal adult E. sinensis , it had opposite effects of reducing precocity in juveniles . This study investigated the effects of dietary PL and HUFA on survival, gonadal development and biochemical composition of precocious E. sinensis . Two diets with PL and HUFA supplementation (diet A) and deficient (diet B) were formulated and fed to precocious E. sinensis . Although no significant differences were found on survival and gonadosomatic index of crabs fed both diets, crabs fed diet B had significantly higher hepatosomatic index and hepatopancrean lipid content than crabs fed diet A. The percentages, 14:0, 18:1n-9, 20:5n-3 and 22:6n-3, in hepatopancreas, muscle and gonads were positively correlated to the diets. Interestingly, the crabs fed diet B accumulated significantly higher 18:2n-6 in gonads and muscle than those fed diet A. Furthermore, substantially higher 20:4n-6 was detected in the gonad and muscle than in the diets. These results suggested that dietary PL and HUFA had limited effects on male gonad biochemical composition. Meanwhile, the precocious E. sinensis may be capable of negating the negative effects of HUFA deficiency by enhanced tissue 18:2n-6 accumulation and converting 18:2n-6 to 20:4n-6.     

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.     

Effect of a dietary phospholipid supplementation on growth and fatty acid composition of European sea bass (Dicentrarchus labrax L.) and turbot (Scophthalmus maximus L.) juveniles from weaning onwards

Two 40-day feeding trials using extruded diets were conducted to assess the effect of a dietary phospholipid (PL) supplementation on growth, survival and fatty acid composition of European sea bass (Dicentrarchus labrax) and turbot (Scophthalmus maximus) from weaning onwards. Two dietary treatments (FO and PL) were tested; both had an identical extruded basis (92.5% total diet weight) coated with a different lipid fraction (7.5% total diet weight). Diet PL contained 2% egg yolk PL (69% pure). In diet FO the PL was replaced by hydrogenated coconut oil. The isolipidic diets contained an equal amount of fish oil ethyl esters providing 1.6% (% diet dry weight) of n-3 highly unsaturated fatty acids (HUFA). A diet water stability test showed no effect of the PL supplementation on the leaching of the dietary fatty acids. In both fish species weight, but not survival, significantly increased as a result of PL supplementation. Weaning onto the experimental diets resulted in similar changes in the relative percent levels of fatty acids in both species. In general, the percentage of saturated fatty acids levelled off after a rapid increase, while monoenes increased after an initial decrease. Total n-3 polyunsaturated fatty acids (PUFA) decreased and total n-6 PUFA remained almost constant. The major effect of the dietary PL on fish fatty acid composition was a 50% increase in n-6 and n-3 HUFAs compared to the PL-free FO diet. The rise in n-6 HUFA may have reflected the higher moiety in the dietary PL. On the other hand this was not the case for the n-3 HUFA since they represented only low levels in the PL fraction (0.1%) compared to that provided by the ethyl esters (1.6%) suggesting a more efficient incorporation of the PL n-3 HUFA than of the ethyl ester n-3 HUFA. A second hypothesis is that the dietary PL may have favored the incorporation of the dietary ethyl ester n-3 HUFA.     

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。     

Growth response,body composition and fatty acid profile of Caspian brown trout (<Emphasis Type="Italic">Salmo trutta Caspius</Emphasis>) juvenile fed diets containing different levels of soybean phosphatidylcholine

We investigated the effects of soybean phosphatidylcholine (PtCho) on the growth, fatty acid (FA) profile, and body composition of juvenile Caspian brown trout. Juvenile trout, initial average weight 0.8 ± 0.12 g, were fed semi-purified formulated diets supplemented with 2, 4, and 6% PtCho for 5 weeks. Results showed that fish with diets containing 4 or 6% PtCho had significantly greater growth. The FA profiles of both the polar lipids (PL) and neutral lipids (NL) in juvenile tissues were influenced by dietary FA, although the effects of PtCho supplementation were more marked for PL than for NL. Fish fed PtCho in the diet also had higher levels of 18:2n-6, 20:4n-6 and n-6, and significantly lower levels of docosahexaenoic acid and eicosapentaenoic acid in both PL and NL. The lipid contents of whole-body tissues and liver were positively affected by PtCho percentage in the diet. Specific growth rate, hepatosomatic index, visceralsomatic index, and protein efficiency ratio were also significantly influenced by dietary PtCho. The results of our study indicate that dietary PtCho has a growth-promoting effect and that juvenile Caspian brown trout have a relatively moderate PtCho requirement (at least 4% dry weight of the diet).     

牙鲆幼鱼对EPA和DHA的营养需求

研究了EPA和DHA水平对牙鲆生长的影响,饲料中含0.5%EPA和1.0%～1.5%DHA能保证牙鲆幼鱼最适生长,鱼体水分最低,肝体指数最小,脂肪含量有较大幅度提高,肝脏极性脂中EPA和DHA达到最大积累;在肝脏和肌肉的非极性脂部分,各组间的脂肪酸组成没有显著变化,而极性脂部分能体现出饲料中n-3 HUFA含量对鱼体脂肪酸组成的影响,极性脂中的EPA和DHA含量远高于非极性脂;在肌肉和肝脏的极性脂和非极性脂中都含有较高的16:0和18:1n-9; 18:1n-9/n-3HUFA可以作为必需脂肪酸满足程度的一个判据,18:1n-9值的升高往往是缺乏必需脂肪酸的表现,在生长最佳时18:1n-9/n-3HUFA比值下降,为0.62和0.74.     

饲料组成对银鲳幼鱼生长率及肌肉氨基酸、脂肪酸组成的影响

研究分析了饲料组成对银鲳(Pampus argenteus)幼鱼特定生长率(SGR)及肌肉氨基酸与脂肪酸组成的影响。实验共设4组不同的饲料组成,依次为饲料A(鱼肉糜)、饲料B(鱼肉糜+配合饲料)、饲料C(鱼肉糜+配合饲料+蛏子肉糜)和饲料D(鱼肉糜+配合饲料+蛏子肉糜+桡足类)。实验用银鲳幼鱼的平均体重为4.80±0.11 g,每组饲料设3重复,实验周期为9周。研究结果显示,不同饲料组成可显著影响银鲳的特定生长率,饲料A组的特定生长率最低,并显著低于其它各饲料组;饲料D组的特定生长率最高,且显著高于饲料B、C组的特定生长率(P<0.05);但饲料B、C组间银鲳特定生长率无显著性差异(P>0.05)。银鲳肌肉氨基酸与脂肪酸的分析结果显示,4组饲料组成对银鲳肌肉氨基酸的组成及含量并无显著性影响(P>0.05),但可显著影响肌肉脂肪酸的组成及含量(P<0.05)。饲料D组的多不饱和脂肪酸(PUFA)、高度不饱和脂肪酸(HUFA)及n-3HUFA含量均分别显著高于饲料A、B和C组(P<0.05),饲料B和C组的PUFA、HUFA及n-3HUFA均分别显著高于饲料A组(P<0.05),但饲料B、C组间并无显著性差异(P>0.05)。综合分析得出,丰富的饲料组成以及饲料中较高的HUFA含量均有利于银鲳幼鱼的生长。     

Polyunsaturated fatty acid metabolism in Atlantic salmon (Salmo salar) undergoing parr-smolt transformation and the effects of dietary linseed and rapeseed oils

Duplicate groups of Atlantic salmon parr were fed diets containing either fish oil (FO), rapeseed oil (RO), linseed oil (LO) or linseed oil supplemented with arachidonic acid (20:4n-6; AA) (LOA) from October (week 0) to seawater transfer in March (week 19). From March to July (weeks 20–34) all fish were fed a fish oil-containing diet. Fatty acyl desaturation and elongation activity in isolated hepatocytes incubated with [1-¹⁴C]18:3n-3 increased in all dietary groups, peaking in early March about one month prior to seawater transfer. Desaturation activities at their peak were significantly greater in fish fed the vegetable oils, particularly RO, compared to fish fed FO. Docosahexaenoic acid (22:6n-3:DHA) and AA in liver and gill polar lipids (PL) increased in all dietary groups during the freshwater phase whereas eicosapentaenoic acid (20:5n-3; EPA) increased greatly in all groups after seawater transfer. The AA/EPA ratio in tissue PL increased up to seawater transfer and then decreased after transfer. AA levels and the AA/EPA ratio in gill PL were generally higher in the LOA group. The levels of 18:3n-3 in muscle total lipid were increased significantly in the LO, LOA and, to a lesser extent, RO groups prior to transfer but were reduced to initial levels by the termination of the experiment (week 34). In contrast, 18:2n-6 in muscle total lipid was significantly increased after 18 weeks in fish fed the diets supplemented with RO and LO, and was significantly greater in the FO and RO groups at the termination of the experiment. Gill PGF production showed a large peak about two months after transfer to seawater. The production of total PGF post-transfer was significantly lower in fish previously fed the LOA diet. However, plasma chloride concentrations in fish subjected to a seawater challenge at 18 weeks were all lower in fish fed the diets with vegetable oils. This effect was significant in the case of fish receiving the diet with LOA, compared to those fed the diet containing FO. The present study showed that during parr-smolt transformation in Atlantic salmon there is a pre-adaptive increase in hepatocyte fatty acyl desaturation/elongation activities that is controlled primarily by environmental factors such as photoperiod and temperature but that can also be significantly modulated by diet. Feeding salmon parr diets supplemented with rapeseed or linseed oils prevented inhibition of the desaturase activities that is induced by feeding parr diets with fish oils and thus influenced the smoltification process by altering tissue PL fatty acid compositions and eicosanoid production. These effects, in turn, had a beneficial effect on the ability of the fish to osmoregulate and thus adapt to salinity changes.     

Lipids of arctic charr,Salvelinus alpinus (L.) I. Dietary induced changes in lipid class and fatty acid composition

Arctic charr (Salvelinus alpinus L.) were fed either a commercial diet or six experimental test diets containing coconut oil and different polyunsaturated fatty acids (PUFA) at a level of 1% by dry weight. Best growth rates were observed with the commercial diet, worst with diet containing coconut oil with no PUFA. An increase in hepatic lipid, hepatic sterol esters and muscular moisture content, and a decrease in muscular lipid was generally found in fish fed the test diets compared to those maintained on the commercial diet.Phosphatidylcholine was the dominant polar lipid (PL) class in all tissues examined. Extensive modification of dietary saturated fatty acids into 18:1 (n-9) was observed in tissue triacylglycerols (TAG) of fish fed test diets. No changes occurred with the commercial diet.Dietary PUFA were essentially incorporated unchanged into tissue TAG of all fish in the present study. PUFA composition of hepatic phospholipids was significantly influenced by that contained in the diets. However both 18:2 (n-6) and 18:3 (n-3) in the test diets were extensively elongated and desaturated prior to incorporation into PL. The (n-9) PUFA content was always higher in liver of fish fed the test diets. When 18:2 (n-6) and 18:3 (n-3) were supplied together, the level of (n-3) PUFA exceeded those of (n-6) PUFA. Muscle PL were less influenced by diet than liver. In muscle (n-3) PUFA were always the predominant PUFA irrespective of diet. Only low amounts of (n-9) PUFA were found. It is suggested that (n-3) PUFA are the prime essential fatty acids for Arctic charr, and that they are used in preference to (n-6) PUFA for elongation, desaturation and incorporation into PL. The results suggest that the quantitative requirement of Arctic charr for EFA is may be higher than that of other salmonids.     

Fatty acids in muscle of wild and farmed red porgy, Pagrus pagrus

The total fat content and the fatty acids of total lipids (TL), phospholipids (PL) and triacylglycerols (TAG) were analysed in white muscle from wild and reared red porgy, Pagrus pagrus (L.). The fat percentage was higher in reared (3.03 ± 0.57%) (mean ± SE) than wild (0.65 ± 0.03%) fish. The fatty acid pattern of reared porgy TL reflected the diet's lipid. Wild red porgy showed higher levels of ω3 and ω6 polyunsaturated fatty acids (PUFA) than reared, but both the atherogenic index and the index of thrombogenicity were very low for both wild and reared red porgy. The lipid fractions showed that the PL were composed of very high levels of PUFA, especially 22:6ω3, and their composition seemed to be better regulated than the composition of TAG. TAG showed greater differences between wild and reared fish, presumably because they reflected the dietary content of lipids. PUFA were the principal component of wild red porgy TAG.     

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.