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.     

Effects of dietary (n-3) and (n-6) polyunsaturated fatty acid ratio on the immune response of Atlantic salmon, Salmo salar L.

To examine the influence of the dietary ratio of (n-3) to (n-6) polyunsaturated fatty acids (PUFAs) on the immune system of Atlantic salmon, Salmo salar L., two dietary trials were carried out in which parr were maintained on diets containing either fish oil [(n-3)/(n-6) PUFA = 5.2] or sunflower oil [(n-3)/(n-6) PUFA = 0.3] and assessed for differences in immunological parameters. There were no significant differences in blood cell counts, differential leucocyte counts or haematocrit values between dietary groups, and while no apparent differences were observed in the non-specific immune parameters measured, there was a significantly higher number of B cells responding to Aeromonas salmonicida, in the kidney and spleen of vaccinated fish maintained on high (n-3)/(n-6) PUFAs diets. There was also a significant difference (P≤ 0.01) between the dietary groups in trial 1 and trial 2 when non-vaccinated fish were challenged with Aeromonas salmonicida and Vibrio anguillarum, respectively, with the (n-6) group succumbing to the bacterium before the (n-3) group. The results suggest that Atlantic salmon fed diets with a low ratio of (n-3)/(n-6) PUFA may be less resistant to infection than those fed diets containing lipid with a high (n-3)/(n-6) PUFA ratio.     

Nutritional evaluation of fatty acids for the open thelycum shrimp, Litopenaeus vannamei: II. Effect of dietary n-3 and n-6 polyunsaturated and highly unsaturated fatty acids on juvenile shrimp growth, survival, and fatty acid composition

This study evaluated the nutritional value of dietary n‐3 and n‐6 polyunsaturated fatty acids (PUFA) such as linoleic (LOA) and linolenic (LNA) acids, and highly unsaturated fatty acids (HUFA) such as arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids for juvenile Litopenaeus vannamei, based on their effects on growth, survival, and fatty acid composition of hepatopancreas and muscle tissue. Diets contained 5% total lipid. A basal diet contained palmitic and stearic acids each at 2.5% of diet. Five diets contained 0.5% dry weight of LOA, LNA, AA, EPA, or DHA. An additional diet evaluated HUFA in combination by supplementing at 0.5% of diet, a mixture of n‐3 HUFA. All HUFA showed higher nutritional value than PUFA for shrimp and produced significantly (P < 0.05) higher final weight, weight gain, and total lipid in shrimp muscle. Fatty acid profiles of shrimp tissues reflected the composition of the dietary lipids. In general, saturated fatty acids were more abundant in the neutral factions, while PUFA and HUFA were more abundant in the polar fractions of tissues. Under these experimental conditions, HUFA had much greater nutritional value than PUFA for juvenile L. vannamei; moreover, dietary requirements for PUFA were not demonstrated.     

Influence of dietary n-3 fatty acids on the desaturation and elongation of [1-14C] 18:2 n-6 and [1-14C] 18:3 n-3 in Atlantic salmon hepatocytes

Atlantic salmon (Salmo salar) were fed diets containing fish oil supplemented with 22:6n-3 (FO diet) or linseed oil supplemented with 20:5n-3 (LO diet) for 6 months. The effects of these diets, both containing about 36% n-3 fatty acids, on the esterification, desaturation and elongation of [1-¹⁴C] 18:2n-6 and [1-¹⁴C] 18:3n-3 were investigated in isolated hepatocytes. The percentages of radioactivity which was esterified from [1-¹⁴C] 18:2n-6 or [1-¹⁴C]18:3n-3 into total lipids, were approximately 20% lower in hepatocytes from fish fed the FO diet than in hepatocytes from fish fed the LO diet. The percentages of radioactivity esterified in both groups were further reduced when 0.1 mM unlabelled 22:6n-3 was added to the incubation. The percentage of desaturation and elongation products formed from [1-¹⁴C] 18:2n-6 was twice as high in hepatocytes from salmon fed the FO diet as it was in hepatocytes from fish fed the LO diet. The ratio of 18:2n-6 to 18:3n-3 was five times higher in the FO diet, and this probably promoted the conversion of 18:2n-6 to longer chain n-6 fatty acids. When 0.1mM unlabelled 22:6n-3 was added to the incubation medium, the percentages of desaturation and elongation products formed were unchanged. Thus, a high level of 22:6n-3 in the diet is apparently not inhibiting the conversion of 18:2n-6 to 20:4n-6, as long as the amount of 18:2n-6 present is substantially higher than that of 18:3n-3. No desaturation and elongation products were recovered from the phospholipids of hepatocytes incubated with [1-¹⁴C] 18:3n-3 in any of the groups. However, the `dead end' elongation product 20:3n-3 was found in the triacylglycerol fraction, and the percentage of this fatty acid increased when 22:6n-3 was added to the incubation medium.     

Organ and phospholipid class fatty acid specificity in response to dietary depletion of essential n‐3 fatty acids in Atlantic salmon (Salmo salar L.)

The cell membrane phospholipid composition is of major importance for normal cell functions. However, it is not known how complete depletion of both shorter and longer chain omega‐3 fatty acids in salmon diets influences fatty acid composition of phospholipid subclasses in different organs of Atlantic salmon. We describe here the fatty acid composition in phospholipid subclasses of liver, muscle, heart and intestine in Atlantic salmon after 18 months of dietary n‐3 essential fatty acids deprivation. The percentage of 22:6n‐3 was markedly reduced in almost all phospholipid subclasses, and except for muscle phosphatidylcholine, phosphatidylethanolamine (PE) and phosphatidylinositol (PI), phospholipids in deficient fish were totally devoid of 20:5n‐3. As compensation, we observed significant increases in 20:4n‐6, and especially in 20:3n‐9 (Mead acid) and 22:5n‐6, varying among phospholipids and organs. High amounts of 20:3n‐9 were found in liver and intestinal PE, little in PE from heart and muscle. For 22:5n‐6, we saw a small incorporation in PI in liver and intestine compared to heart and muscle. Generally in PI, the preference for 20:4n‐6 to 20:5n‐3 differed significantly between organs. Overall, changes upon n‐3 deprivation seemed to be strongest in liver and intestine, the lipid‐secreting organs, and less in muscle and heart.     

Cholesterol and short-chain fatty acids in diets for Atlantic salmon Salmo salar (L.): effects on growth, organ indices, macronutrient digestibility, and fatty acid composition

The influence of dietary cholesterol (CHOL) and short-chain fatty acids (SCFA; sodium salts of acetic, propionic and butyric acid, 5:5:2 w/w/w) on growth, organ indices, macronutrient digestibility, and fatty acid composition of Atlantic salmon Salmo salar was investigated. Salmon (initial average weight 0.7 kg) held in seawater (7°C) for 175 days were fed one of six diets: 1, without CHOL/SCFA supplement; 2, with 0.5% SCFA; 3, with 2.0% SCFA; 4, with 1.0% CHOL; 5, with 1.0% CHOL and 0.5% SCFA; 6, with 1.0% CHOL and 2.0% SCFA.
Neither SCFA nor CHOL supplements had any significant effects on specific growth rate (SGR), mortality, apparent digestibility coefficients (ADC) of macronutrients, total lipid content. Hepatosomatic index (HSI) was slightly increased in salmon fed the CHOL supplement ( P  < 0.05). Hepatic CHOL concentration, but not the hepatic CHOL pool, was significantly increased ( P  < 0.001) by dietary CHOL supplementation.
The fatty acid compositions of fillet and gut tissues were not influenced by dietary treatment, while significant effects of CHOL supplements were observed in faeces and liver. Less saturated fatty acids and more mono- and poly-unsaturated fatty acids were excreted with faeces in salmon fed CHOL supplements. Salmon fed CHOL supplements significantly reduced the relative concentration of hepatic palmitic acid (C16 : 0), arachidonic acid (C20 : 4 n-6) and docosahexaenoic acid (C22 : 6 n-3), while the contents of oleic acid (C18 : 1 n-9) and eicosenoic acid (C20 : 1 n-9) were significantly increased. SCFA did not influence the observed effects of dietary CHOL.
The present study shows that dietary CHOL supplements profoundly altered excretion and liver metabolism of individual fatty acids in salmon. The impact of this alteration on physiological performance has not been elucidated.     

Temperature modulates liver lipid accumulation in Atlantic salmon (Salmo salar L.) fed low dietary levels of long‐chain n‐3 fatty acids

Atlantic salmon (Salmo salar) were fed five graded levels of eicosapentaenoic acid (EPA, 20:5n‐3) and docosahexaenoic acid (DHA, 22:6n‐3), from 1.4 to 5.2% of total fatty acids (FA, 5–17 mg kg^?1 feed), and grew from ~160 g to ~3000 g, with the period from 1450 g onwards conducted both at 6 °C and at 12 °C. All fish appeared healthy, and there were no diet‐related differences in haematological or plasma parameters, as well as intestinal histological or gut microbiota analysis. Fish reared at 6 °C had higher accumulation of storage lipids in the liver compared to fish reared at 12 °C. Liver lipids also increased with decreasing dietary EPA + DHA at 6 °C, while there was no such relationship at 12 °C. Gene expression of SREBP1 and 2, LXR, FAS and CPT1 could not explain the differences in liver lipid accumulation. In liver polar lipids, DHA was found to be reduced when dietary EPA + DHA was <2.7% of FAs, while the level of EPA in the membranes was not affected. In conclusion, reducing dietary EPA + DHA from 5.2 to 1.4% of total FAs had a minor impact on fish health. Temperature was the factor that most affected the liver lipid accumulation, but there was also an interaction with dietary components.     

Effects of dietary protein, and fat level and rapeseed oil on growth and tissue fatty acid composition and metabolism in Atlantic salmon (Salmo salar L.) reared at low water temperatures

A 12‐week feeding trial was conducted to elucidate the interactive effects of dietary fat, protein contents and oil source on growth, whole body proximate composition, protein productive value (PPV) and fatty acid (FA) composition of muscle and liver in Atlantic salmon (Salmo salar L.)` at low water temperatures (4.2 °C). Triplicate groups of Atlantic salmon (initial weight 1168 g) were fed six isoenergetic diets, formulated to provide either 390 g kg⁻¹ protein and 320 g kg⁻¹ fat (high‐protein diets) or 340 g kg⁻¹ protein and 360 g kg⁻¹ fat (low‐protein diets). Within each dietary protein/fat level, crude rapeseed oil (RO) comprised 0, 30 or 60% (R0, R30, R60, respectively) of the added oil. After 12 weeks, the overall growth and feed conversion ratio (FCR) were very good for all treatments [thermal growth coefficient (TGC): 4.76 (±0.23); FCR: 0.85 (±0.02)]. Significant effects were shown owing to the oil source on specific growth rate and TGC only. The liver and muscle FA compositions were highly affected by the graded inclusion of RO. The PPV was significantly affected by the dietary protein level. The results of this study suggest that more sustainable, lower protein diets with moderate RO inclusion can be used in Atlantic salmon culture at low water temperatures with no negative effects on growth and feed conversion, no major detrimental effects on lipid and FA metabolism and a positive effect on protein sparing.     

Influence of dietary lipid composition on cardiac pathology in farmed Atlantic salmon, Salmo salar L

The present study investigated the short-term (5 months) effect of replacing dietary marine oils with vegetable oils on the development of arteriosclerotic changes in the heart of Atlantic salmon, Salmo salar. The experiment was performed as a randomized observer-blinded and controlled trial. Farmed Atlantic salmon were randomly sampled from a study population containing 900 individuals. The salmon were divided into three groups and given diets with either 100% fish oil (Diet 1), a 50/50% mixture of fish oil and rapeseed oil (Diet 2) or 100% rapeseed oil (Diet 3). Ten sexually immature salmon from each dietary group were sampled in March and August 2002. Additionally, 47 sexually mature wild salmon were randomly collected in mid-September 2001. Serial histological sections were taken from the bulbus arteriosus and ventricle wall for histopathological evaluation of the coronary arteries and myocardium. No significant differences in mean coronary changes recorded by the main variable 'mean range lesion' (MRL) were detected between the groups in March or August. MRL increased significantly between March and August with Diet 2 (P < 0.01), was nearly significant with Diet 3 (P = 0.06) and was unchanged with Diet 1. This pattern coincided with the Diet 2 group having the highest increase in heart weight. MHC class II immunoreactive cells in the coronary changes were detected in sections from one individual in each group. Heart weight was the most dominant variable in the data set and explained linearly 15.5% of the variation in MRL. Body weight, fish length and heart weight were all significantly, positively and linearly correlated to MRL. The Diet 2 group had the highest growth rate and also exhibited a significant increase in MRL. The possible influence of diet composition on weight gain and MRL needs to be further elucidated. Increase in heart weight seems to be the dominating predictor of the appearance of MRL in Atlantic salmon. However, the present results cannot exclude the possibility that differences in fatty acid composition of fish feed can influence the development of arteriosclerotic changes in Atlantic salmon.     

Incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids in phospholipid classes in cultured turbot (Scophthalmus maximus) cells

The incorporation and metabolism of various (n-3) and (n-6) polyunsaturated fatty acids (PUFA) supplemented to the culture medium was investigated in a turbot cell line (TF). The distribution, and the occurrence and extent of further metabolism of incorporated PUFA via desaturation/elongation mechanisms in specific phospholipid classes was determined from the different fatty acid compositions. The cells contained Δ6 and Δ4 desaturase activities but were generally deficient in C18–20 elongase activity. Δ5 Desaturase activity was generally masked by this deficiency but was present. The compositional data indicated that there was a high degree of specificity between individual phospholipid classes and particular fatty acids probably driven by the specificities of the acylating enzymes. The highest percentages of the supplemented acids were generally observed in the phosphatidic acid/cardiolipin fraction (PA/CL), suggesting a role for PA in the incorporation of the supplemented acids into the phospholipid pool. PI had a characteristic composition consistent with a putative role as a pool of precursor fatty acid for eicosanoid synthesis. Mechanisms were evident for generating and/or maintaining this composition.     

Long-term effects of dietary fat level and feeding rate on growth, feed utilization and carcass quality of Atlantic salmon

Two extruded diets designed to have fat levels of 220 g kg⁻¹ (F22) and 300 g kg⁻¹ (F30) were fed to Atlantic salmon Salmo salar L. in two different experiments during the sea rearing period (from 0.2–0.3 kg to 3–4 kg). Each diet was fed restricted and isoenergetically at two feeding rates to fish in triplicate groups. In one of the experiments, a supplementary group of fish was fed to satiation with the F30 diet. All fish were slaughtered and evaluated for quality according to a commercial standard.
No difference in growth was observed between fish fed the two diets at similar feeding rates and the growth was proportional to the amount of dietary energy offered. Feed conversion ratios decreased according to higher energy content in the F30 diet, and the nitrogen and phosphorus retention increased significantly. Fish fed the F30 diet revealed a higher incidence of sexual maturity. Fat content in cutlets and dressed carcasses were significantly affected by feeding rate but not by dietary fat level. Fish fed the F30 diet had more visceral fat and, consequently, lower dress-out percentage. Mortality, liver size and liver colour were not significantly affected by dietary fat level.
These experiments showed that even large differences in dietary fat level employed for the entire sea rearing period of Atlantic salmon, did not, or only marginally affected the cutlet and dressed carcass fat content. The high fat diet improved the feed utilization, thus decreasing the discharge to the environments. Furthermore, it resulted in greater growth at ad libitum feeding.     

Effect of replacing dietary fish oil with soybean oil on production performance and fillet lipid and fatty acid composition of juvenile cobia Rachycentron canadum

As a marine carnivore exhibiting exceptionally high growth rates, cobia are considered a species for which fish oil (FO) replacement may be difficult. However, partial, if not complete, FO replacement is necessary to ensure sustainability. We evaluated the effects of graded substitution of dietary FO with soybean oil (SO) in cobia culture. Feeds contained FO (100% FO), SO (0% FO) or blends of the two (67% FO, 33% FO) as the supplemental lipid source. Production performance was largely unaffected by partial replacement of FO with SO: feed intake and final weight were reduced only in the 0% FO dietary treatment. Fillet total lipid fatty acid (FA) composition differed among the dietary treatments, closely approximating dietary FA profile. As increasing amounts of FO were replaced, SO‐associated FA became enriched within the fillet lipid at the expense of FO‐associated FA. Fillet lipid classes were associated with a particular FA signature, regardless of dietary FA profile. SO can replace a substantial amount of dietary FO; however, juvenile cobia appear to exhibit a nominal requirement for intact long‐chain polyunsaturated FA. Therefore, aggressive FO replacement may result in essential fatty acid deficiencies unless the feeds can be amended with alternative sources of these essential nutrients.     

The fatty acid compositions of total,neutral and polar lipids in wild and farmed lambari (Astyanax altiparanae) (Garutti & Britski, 2000) broodstock

One way to develop broodstock fish diets is to determine the compositions of wild broodstock tissues and attempt to replicate these compositions in the eggs of farmed fish via dietary manipulation. We collected 30 wild and 30 farmed lambari females that were in the reproductive stage. The extraction and separation of polar and neutral fractions and the saponification and methylation of lipids were performed and analysed in the muscles, livers and ovaries to determine the compositions of the fatty acids via gas chromatography. Regardless of habitat, lambaris mobilize large amounts of fat to the ovaries during the reproductive period, in addition to highly unsaturated fatty acids, such as arachidonic, eicosapentaenoic and docosahexaenoic acids. The wild lambaris were observed to contain higher levels of various fatty acids, including linoleic acid, which is an essential fatty acid. The most abundant fatty acid that was observed in the commercial diet was linoleic acid, which was supplied in all fish farmed tissues. The commercial diet has low AA, EPA and DHA contents, and, higher levels of these fatty acids were recorded in the tissues of farmed lambari, which suggests that this species are able to elongate and desaturate precursors, linoleic and linolenic acids, into highly unsaturated fatty acids.     

Influence of dietary palm oil on growth, tissue fatty acid compositions, and fatty acid metabolism in liver and intestine in rainbow trout (Oncorhynchus mykiss)

This study aimed to investigate the effects of dietary crude palm oil (CPO) on fatty acid metabolism in liver and intestine of rainbow trout. Triplicate groups of rainbow trout for 10 weeks at 13 °C were fed on diets in which CPO replaced fish oil (FO) in a graded manner (0–100%). At the end of the trial, fatty acid compositions of flesh, liver and pyloric caeca were determined and highly unsaturated fatty acid (HUFA) synthesis and fatty acid oxidation were estimated in isolated hepatocytes and caecal enterocytes using [1‐¹⁴C]18:3n‐3 as substrate. Growth performance and feed efficiency were unaffected by dietary CPO. Fatty acid compositions of selected tissues reflected the dietary fatty acid composition with increasing CPO resulting in increased proportions of 18:1n‐9 and 18:2n‐6 and decreased proportions of n‐3HUFA, 20:5n‐3 and 22:6n‐3. Palmitic acid, 16:0, was also increased in flesh and pyloric caeca, but not in liver. The capacity of HUFA synthesis from 18:3n‐3 increased by up to threefold in both hepatocytes and enterocytes in response to graded increases in dietary CPO. In contrast, oxidation of 18:3n‐3 was unaffected by dietary CPO in hepatocytes and reduced by high levels of dietary CPO in enterocytes. The results of this study suggest that CPO can be used at least to partially replace FO in diets for rainbow trout in terms of permitting similar growth and feed conversion, and having no major detrimental effects on lipid and fatty acid metabolism, although flesh fatty acid compositions are significantly affected at an inclusion level above 50%, with n‐3HUFA reduced by up to 40%.     

Effects of dietary n−3 polyunsaturated fatty acids on lipid and fatty acid composition and haematology of juvenile Arctic charr Salvelinus alpinus (L.)

The effect of dietary n−3 and n−6 polyunsaturated fatty acids (PUFAs) on juvenile Arctic charr Salvelinus alpinus (L.) were investigated with respect to essential fatty acid (EFA) deficiency and lipid metabolism using one commercial and 12 casein-based test diets. Arctic charr with mean weight of 1.6g were fed test diets for 12 weeks at 10°C. At the end of the feeding, blood, liver, muscle and whole fish were sampled to determine haematocrit, haemoglobin, water content, lipid and fatty acid composition. Charr fed diets containing 0–1.0% n−3 PUFAs showed typical EFA deficiency signs: fatty liver or elevated water content in whole body or substantial accumulation of 20:3n−9 in liver polar lipids. These signs were less apparent or disappeared when charr were fed diets containing ≥ 2.0% 18:3n−3. No correlation was found between dietary PUFAs and haematocrit or haemoglobin values. Significant changes in fatty acid composition of liver polar lipids in charr fed dietary PUFAs indicate that charr can convert 18:3n−3, 18:2n−6 and 20:5n−3 into long-chain PUFAs. While charr had a direct incorporation of dietary 22:6n−3 into liver and muscle there appears to be preferential utilization of n−3 PUFAs for elongation and desaturation. The conversion of 18:4n−3 was less in muscle than in livers. These findings, combined with data on growth and feed efficiency reported previously by Yang and Dick (1993), indicate that charr require 1−2% dietary 18:3n−3 (dry weight). Small amounts of dietary 18:2n−6 (up to 0.7%) did not have detrimental effects on charr.     

Effects of dietary levels of 20:5n-3 and 22:6n-3 on tissue lipid composition in juvenile Atlantic salmon, Salmo salar, with emphasis on brain and eye

Four dietary groups of juvenile Atlantic salmon, Salmo salar L., each with three replicates, were fed diets with increasing levels of docosahexaenoic acid (22:6n-3; DHA) and eicosapentaenoic acid (20:5n-3; EPA). Fatty acid composition of brain and eye was determined at the start and approximately every 3 weeks during the experimental period, and fatty acid composition of liver and fillet was determined in fish from the final sampling. Lipid class composition of brain and eye, and fatty acid composition of these lipid classes was determined at the end of the experiment. There was no effect of increasing dietary DHA content on fatty acid composition, lipid class composition or DHA levels in the lipid classes in the juvenile Atlantic salmon brain. The increasing dietary EPA content, however, was reflected in both the total fatty acid composition and in the EPA content in neutral lipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI). A minor effect of the increasing dietary DHA content was found in the lipid composition of the juvenile salmon eye. Both EPA and 18:2n-6 levels in eye, however, clearly reflected the increasing and decreasing, respectively, dietary levels of these two fatty acids. The dietary EPA levels also affected the EPA levels in neutral lipids, PC, PE, PI and PS (phosphatidylserine) in the juvenile salmon eye. The results demonstrate that these dietary levels of DHA had no effect on brain lipid composition and only a minor effect on eye lipid composition. Furthermore, the dietary EPA levels significantly affected the lipid composition of both brain and eye. The fillet fatty acid composition reflected the dietary fatty acid composition, except for the DHA/EPA ratio, which was reversed in fillet compared with that in the diets. The liver fatty acid composition was also affected by the increasing dietary EPA and DHA levels.     

Nutritional evaluation of fatty acids for the open thelycum shrimp, Litopenaeus vannamei: I. Effect of dietary linoleic and linolenic acids at different concentrations and ratios on juvenile shrimp growth, survival and fatty acid composition

A 6‐week feeding trial was conducted to evaluate the nutritional value of dietary linoleic (18:2n‐6, LOA) and linolenic (18:3n‐3, LNA) acids for juvenile Litopenaeus vannamei by determining their effects on growth, survival and fatty acid composition of hepatopancreas and muscle tissue. Diets were formulated to contain 5% total lipid. A basal diet contained only palmitic and stearic acids, each at 2.5% of diet. Six diets contained one of three levels (0.25, 0.5 and 1%) of either LOA or LNA, and three diets had different ratios of LNA/LOA (1, 3, 9) at a combined inclusion level of 0.5% of diet. An additional diet contained 0.5% of a mixture of n‐3 highly unsaturated fatty acids (HUFA). The fatty acid profile of hepatopancreas and muscle of shrimp reflected the profile of the diets. HUFA of the n‐3 family showed higher nutritional value than LOA or LNA for juvenile L. vannamei by producing significantly (P < 0.05) higher final weight and weight gain. Neither LOA nor LNA, alone or in combination, improved growth significantly compared with shrimp fed the basal diet.Thus, dietary requirements for LOA and LNA were not demonstrated under these experimental conditions.     

Effects of dietary docosahexaenoic acid (22:6n‐3) and arachidonic acid (20:4n‐6) on the growth,survival, stress resistance and fatty acid composition in black sea bass Centropristis striata (Linnaeus 1758) larvae

The objectives of this study were to determine the effects of the dietary docosahexaenoic acid (DHA) to arachidonic acid (ARA) ratio on the survival, growth, hypersaline stress resistance and tissue composition of black sea bass larvae raised from first feeding to metamorphic stages. Larvae were fed enriched rotifers Brachionus rotundiformis and Artemia nauplii containing two levels of DHA (0% and 10% total fatty acids=TFA) in conjunction with three levels of ARA (0%, 3% and 6% TFA). On d24ph, larvae fed the 10:6 (DHA:ARA) treatment showed significantly (P<0.05) higher survival (62.3%) than larvae fed 0:0 (DHA:ARA) (27.4%). Notochord length and dry weight were also significantly (P<0.05) greater in the 10:6 (DHA:ARA) treatment (8.65 mm, 2.14 mg) than in the 0:0 (DHA:ARA) (7.7 mm, 1.65 mg) treatment. During hypersaline (65 g L⁻¹) challenge, no significant differences (P>0.05) were observed in the median survival time (ST50) between larvae fed 10% DHA (ST50=25.6 min) and larvae fed 0% DHA (ST50=18.2 min). The results suggested that black sea bass larvae fed prey containing 10% DHA with increasing ARA within the range of 0–6% showed improved growth and survival from first feeding through metamorphic stages.     

Effects of temperature and dietary n-3 and n-6 fatty acids on endocytic processes in isolated rainbow trout (Oncorhynchus mykiss,Walbaum) hepatocytes

Effects of different incubation temperatures (2, 8, 14 and 20°C) and hepatocyte membrane fatty acid composition on the rate of internalization and lysosomal degradation of the ligand, mannosylated albumin, that is taken up by receptor-mediated endocytosis, were investigated in rainbow trout (Oncorhynchus mykiss, Walbaum). The fish were kept at a water temperature ranging from 9 to 14°C and fed pelleted diets coated with either capelin oil (control), EPA/DHA-concentrate (rich in n-3 polyunsaturated fatty acids) or soybean oil (rich in n-6 unsaturated fatty acids) for at least 3 months prior to sampling. The endocytic uptake mediated by the mannose receptor was very efficient at all temperatures studied. Lysosomal degradation, on the other hand, came to a halt below 8°C. The activation energies for uptake and degradation were 54.6 and 164.2 kJ/mol respectively. No negative effects of increased amounts of either n-3 or n-6 fatty acids were observed on the endocytic parameters studied. On the contrary, multivariate analysis indicated a positive relationship between high levels of n-6 fatty acids and low unsaturation index in the phosphatidylcholine (PC) fraction of the hepatocytes and the internalization rate of 2°C, meaning that the rate of receptor-mediated endocytosis may be affected by membrane fatty acid composition.     

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。