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.     

Chemical Composition of Fresh and Salted Lumpfish (Cyclopterus lumpus) Roe

The original "Eskimo" cardiovascular health benefit of omega-3 fatty acids was ascribed to EPA (eicosapentaenoic acid). The two readily available fish body oils (from U.S. menhaden and Japanese sardines) have approximately 180 mg of EPA/gram, accompanied by much less (120 mg) DHA (docosahexaenoic acid). The EPA was recognized as the source of a prostaglandin (PGI₃) acting as an agent to keep the vascular walls soft and flexible, thus hindering atherosclerosis and vascular constriction, but DHA presented a problem as no such role for it was known. Australian researchers identified DHA as preventing cardiac arrhythmia because they used tuna body oil (DHA ~5 x EPA) in their research. Generally our analyses of salmon muscle triglycerides seem to show DHA > EPA. Total salmon muscle lipids in fillets obtain extra DHA from phospholipids. In the United Kingdom an official medical body now recommends eating fish twice a week and "oily" fish once a week. Examination of DHA for a legitimate health claim in the cardiovascular system, and in infant neural developments and nutrition, and maternal nutrition, offers an alternative market exploiting the most recent developments. These matters should be investigated by the salmon aquaculture industry.     

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.     

Effects of dietary <Emphasis Type="Italic">n</Emphasis>-3 fatty acids on Toll-like receptor activation in primary leucocytes from Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)

The shortage of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the international markets has led to increasing substitution of fish oil by plant oils in Atlantic salmon (Salmo salar) feed and thereby reducing the EPA and DHA content in salmon. However, the minimum required levels of these fatty acids in fish diets for securing fish health are unknown. Fish were fed with 0, 1 or 2% EPA or DHA alone or in combination of both over a period, growing from 50 to 400 g. Primary head kidney leucocytes were isolated and stimulated with Toll-like receptor (TLR) ligands to determine if EPA and DHA deficiency can affect expression of important immune genes and eicosanoid production. Several genes related to viral immune response did not vary between groups. However, there was a tendency that the high-level EPA and DHA groups expressed lower levels of IL-1β in non-stimulated leucocytes. These leucocytes were also more responsive to the TLR ligands, inducing higher expression levels of IL-1β and Mx1 after stimulation. The levels of prostaglandin E2 and leukotriene B4 in serum and media from stimulated leucocytes were lower in both low and high EPA and DHA groups. In conclusion, leucocytes from low EPA and DHA groups seemed to be less responsive towards immunostimulants, like TLR ligands, indicating that low levels or absence of dietary EPA and DHA may have immunosuppressive effects.     

High n‐3 HUFA levels in the diet of Atlantic salmon affect muscle and mitochondrial membrane lipids and their susceptibility to oxidative stress

Atlantic salmon were fed one of four diets with increasing levels (11–58%of total fatty acids (FAs)) of n‐3 highly unsaturated FAs (HUFAs) in order to investigate the effect on muscle and mitochondrial membrane lipids and their susceptibility to oxidative stress. The high n‐3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) groups contained lower percentages of sphingomyelin and cardiolipin in total muscle than the intermediate n‐3 HUFA group. Cardiolipin and sphingomyelin are particularly susceptible to peroxidation, and a reduced percentage of these lipids showed that mitochondrial membranes had been damaged by oxidation. The intermediate n‐3 HUFA group had the highest level of mitochondrial integrity and tendencies of lower thiobarbituric acid reactive substances (TBARS) level than the other dietary groups. The high caspase‐3 activity, in addition to casp3a and bax gene expression levels, in the n‐3 DHA group also suggests that some degree of oxidative stress had occurred. Electron microscopy images showed a higher degree of myofibre–myofibre detachment in fish fed the high HUFA diets than in fish fed the intermediate n‐3 HUFA diet. Our findings show that intermediate levels of n‐3 HUFAs in salmon diets gave the best protection against oxidative damage of mitochondrial membranes and muscle structure.     

Chemical Characterization of Testes Meals Made from Alaska's Seafood Processing Byproducts

ABSTRACT

Our objective was to produce a unique feed ingredient from underutilized walleye pollock (Theragra chalcogramma) and pink salmon (Oncorhynchus gorbuscha) testes. Protein content in meals from both species (72% and 80%, respectively) were above the values found in high quality herring meals (～70%), but both were poor in some essential amino acids, e.g., methionine. Additionally, both were good sources of the amino acid taurine (1.7 and 2.2% of meal, respectively). Pollock meal was very rich in phospholipids (82% of total lipids) and in DHA (28 mg/g meal) and EPA (18 mg/g meal), indicating potential as an ingredient in larval starter diets. The purine contents in both pollock and salmon testes meals were more than 10 times the concentrations found in other fish byproducts or commercial fishmeals. The high concentrations of purines found in these testes, especially in the salmon meal, make it an ideal candidate for an immune system stimulant when added to dietary formulations.     

Effects of dietary vegetable oils and varying dietary EPA and DHA levels on intestinal lipid accumulations in Atlantic salmon

High dietary content of vegetable oil (VO) has been associated with increased intestinal lipid accumulations in fish. The extent of this in aquacultured Atlantic salmon (Salmo salar L.) and its health effects are not certain. Samples were therefore collected from two separate feeding trials to investigate the effect of high dietary VO on intestinal lipid accumulations in Atlantic salmon. In the first trial, the fish were fed diets high in plant protein and with fish oil or ~80% of the fish oil replaced with either olive oil, rapeseed oil or soybean oil in a land‐based experimental set‐up. The second trial was performed in sea cages under commercial production conditions, and the fish were fed two dietary concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (9.7% or 5.5% EPA + DHA of total fatty acids). Neither dietary VO nor variations in EPA and DHA led to any significant effects on intestinal health or lipid accumulations. There were, however, indications of a delayed lipid transport in the rapeseed oil‐fed fish of the first trial, possibly caused by high dietary ≥18‐carbon fatty acids and low dietary 16:0 fatty acid and cholesterol.     

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.     

Variation in Rainbow Trout,Oncorhynchus mykiss,to Biosynthesize Eicosapentaenoic Acid and Docosahexaenoic Acid When Reared on Plant Oil Replacement Feeds

To determine the potential for improving the conversion and deposition of the omega‐3 fatty acids docosahexaenoic acid (DHA; 22:6n‐3) and eicosapentaenoic acid (EPA; 20:5n‐3) in fish, 44 families of rainbow trout were fed a diet low in these components and then evaluated for their ability to convert and store plant oils that did not contain DHA and EPA in their muscle tissue. The range for EPA and DHA detected in the tissues of different families varied between 1.2 and 2.9%, and 3.8 and 7.1% total fatty acid, respectively. After adjusting for covariates, an averaged heritability of 0.78 ± 0.11 for DHA and 0.61 ± 0.17 for EPA was calculated. Expression analysis of genes related to the elongation and conversion of lipids were also analyzed, and significant differences were found in the expression of some genes between groups of families that were delineated as having relative high, medium, and low capabilities of depositing EPA and DHA in their muscle tissue after being reared on the mainly soy/flax oil containing diet. However, none of these genes showed a positive correlation with the high conversion/deposition group .     

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.     

Interactions between dietary docosahexaenoic acid and other long-chain polyunsaturated fatty acids on performance and fatty acid retention in post-smolt Atlantic salmon (Salmo salar)

A study with varying dietary inclusion levels (1, 5, 10, 15 and 20 g kg^?1) of docosahexaenoic acid (DHA; 22:6n-3) was conducted with post-smolt (111 ± 2.6 g; mean ± S.) Atlantic salmon (Salmo salar) over a 9-week period. In addition to the series of DHA inclusion levels, the study included further diets that had DHA at 10 g kg^?1 in combination with either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), both also included at 10 g kg^?1. An additional treatment with both EPA and DHA included at 5 g kg^?1 (total of 10 g kg^?1 long-chain polyunsaturated fatty acids, LC-PUFA) was also included. After a 9-week feeding period, fish were weighed, and carcass, blood and tissue samples collected. A minor improvement in growth was seen with increasing inclusion of DHA. However, the addition of EPA further improved growth response while addition of ARA had no effect on growth. As with most lipid studies, the fatty acid composition of the whole body lipids generally reflected that of the diets. However, there were notable exceptions to this, and these implicate some interactions among the different LC-PUFA in terms of the fatty acid biochemistry in this species. At very low inclusion levels, DHA retention was substantially higher (~250 %) than that at all other inclusion levels (31–58 %). The inclusion of EPA in the diet also had a positive effect on the retention efficiency of DHA. However, EPA retention was highly variable and at low DHA inclusion levels there was a net loss of EPA as this fatty acid was most likely elongated to produce DHA, consistent with increased DHA retention with additional EPA in the diet. Retention of DPA (22:5n-3) was high at low levels of DHA, but diminished with increasing DHA inclusion, similar to that seen with DHA retention. The addition of EPA to the diet resulted in a substantial increase in the efficiency of DPA retention; the inclusion of ARA had the opposite effect. Retention of ARA was unaffected by DHA inclusion, but the addition of either EPA or ARA to the diet resulted in a substantial reduction in the efficiency of ARA retention. No effects of dietary treatment were noted on the retention of either linolenic (18:3n-3) or linoleic (18:2n-6) acids. When the total n-3 LC-PUFA content of the diet was the same but consisted of either DHA alone or as a combination of EPA plus DHA, the performance effects were similar.     

Importance of dietary arachidonic acid for the growth,survival and stress resistance of larval European sea bass (Dicentrarchus labrax) fed high dietary docosahexaenoic and eicosapentaenoic acids

Together with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), arachidonic acid (ARA) is being considered to be an essential fatty acid in marine fish larval diets. The objective of the present study was to determine the importance of dietary ARA levels for larval European sea bass performance, when EPA and DHA are also present in the diet. Eighteen‐day‐old larvae were fed, for 14 days, gelatine‐based microdiets containing the following ARA levels: 0.3%, 0.6% or 1.2%. Elevation of dietary ARA up to 1.2% showed a positive correlation with larval survival and a significant improvement in the specific growth rates, body weight and total length. Arachidonic acid was efficiently incorporated into larval lipids, even at a higher proportion than that in the diets. Increased accumulation of ARA did not affect the incorporation of DHA or EPA from the diet into larval total lipids. A significant positive correlation was found between dietary ARA levels and survival after handling stress, indicating the importance of this fatty acid in sea bass larvae response to acute stressors. The results show the importance of ARA for sea bass larvae, but higher dietary levels should be tested to determine whether there is a negative effect of ARA in sea bass as reported for other species.     

The effect of vitamins C and E in (n-3) highly unsaturated fatty acids-enriched Artemia nauplii on growth, survival, and stress resistance of fresh water walleye Stizostedion vitreum larvae

This study aimed to evaluate the effect of enriching Artemia nauplii with vitamin C (ascorbyl-6 palmitate) or vitamin E (α-tocopherol acetate), 20% w/w, together with a mixture of concentrated eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) on the growth, survival, and stress resistance of fresh water walleye Stizostedion vitreum larvae. Either cod liver oil (CLO) or EPA/DHA ethyl esters concentrate was used as lipid sources in the Artemia enrichment. Walleye larvae were fed ad libitum for 40 days. At day 40, submersion in salt water (25 g L⁻¹) was performed to evaluate larvae resistance to stress. EPA and DHA levels in walleye juveniles fed EPA/DHA-enriched Artemia increased significantly, by an average of 650% compared with fish fed non-enriched Artemia . A significant increase was found for vitamins C (71.8 ± 1.0 and 42.7 ± 1.2 μg g⁻¹ wet weight (WW)) and E (17.0 ± 3.7 and 6.5 ± 0.9 μg g⁻¹WW) concentrations in fish fed enriched and unenriched Artemia , respectively. Growth was comparable throughout treatments, whereas survival was significantly higher in fish fed CLO-enriched Artemia nauplii compared with fish fed Artemia nauplii enriched with EPA/DHA concentrate. The addition of vitamin C increased fish survival by 1.4-fold compared with fish fed Artemia enriched with only EPA/DHA concentrate. The survival of the latter was similar to control fish ( Artemia without enrichment). The supplementation of vitamin E did not affect fish survival significantly. Stress tests revealed that the resistance of walleye larvae to salinity changes increased when Artemia enrichment was supplemented with vitamin C. However, walleye larvae fed CLO-enriched Artemia had the best performances in the stress test.     

Lipid Oxidation and Omega-3 Fatty Acid Retention in Salmon and Mackerel Nuggets During Frozen Storage

The extent of lipid oxidation and retention of omega (ω)-3 fatty acids in milk protein concentrate (MPC)-added mackerel and salmon mince and nuggets during 4-months frozen storage were investigated in order to develop high ω-3 seafood products. Mechanically deboned fish mince formulated with MPC and other ingredients was formed into batter-breaded nuggets with or without par-frying. The addition of MPC at 4% resulted in significantly lower thiobarbituric acid reactive substances (TBARS) values and helped retain significantly (p < 0.05) higher amounts of docosahexaenoic acid (DHA) in both salmon and mackerel mince and eicosapentaenoic acid (EPA) in the mackerel mince. There were no significant differences in peroxide values (PV) and TBARS values between nugget products with and without par-frying. EPA and DHA were retained less in par-fried than raw nuggets probably due to oil leaching and thermal degradation during frying. The reductions of EPA and DHA in salmon were 67% and 53% for raw and 57% and 39% for par-fried nuggets, while in mackerel they were 63% and 73% for raw and 57% and 56% for par-fried nuggets, respectively. Results suggest that although MPC provided some protection against lipid oxidation, additional measures are needed to improve retention of ω-3 fatty acids in mince-based seafood products during frozen storage.     

Comparison of fatty acid contents of wild and cultured rainbow trout <Emphasis Type="Italic">Onchorhynchus mykiss</Emphasis> in Turkey

Abstract:   The total lipid content and fatty acid composition were determined in the flesh and skin of wild and cultured rainbow trout in Turkey. The effect of diet content was also investigated on cultured trout. Gas chromatography-mass spectrometry (GC-MS) was used for fatty acid analyses. Total lipid content of skin was higher than flesh in both types and when compared appreciably higher in cultured fish. The predominant fatty acid was palmitic acid (C16:0) in saturated fatty acids and oleic acid (C18:1n-9) in monounsaturated fatty acids. The amount of eicosapentaenoic acid was double in wild and docosahexaenoic acid (DHA) 1.5 times higher in cultured fish flesh. The n-3/n-6 ratio was higher in cultured fish than wild fish. The levels of palmitic, oleic, linoleic (C18:2n-6) and palmitoleic (C16:1n-7) acids were high in skin. The level of EPA was the same in skin of wild fish but 5.5 times higher in cultured fish, whereas the proportion of DHA in skin was lower for wild and 3.5 times higher in cultured fish. Wild fish had a high level of linoleic, arachidonic (C20:4n-6) and linolenic (C18:3n-3) acids. The total amount of n-3 and n-6 polyunsaturated fatty acids was higher in flesh of wild fish than cultured fish, contrary to skin of cultured fish. The data obtained demonstrated that fatty acid composition of cultured fish did not depend on that of feed.     

Dietary lipids and temperature interact to influence tissue fatty acid compositions of Atlantic salmon, Salmo salar L., parr

Fatty acid compositions of both the polar phospholipids (PLs) and the non‐polar neutral lipids (NLs) in fish tissues are influenced by dietary fatty acids, and tissue fatty acid compositions also change during thermal acclimation. The interaction between these factors in governing fatty acid compositions has been little studied, even though this may have importance when fish are reared in cold water. An experiment was conducted to investigate the effects of temperature (2 vs. 8°C), dietary oil source (fish oil vs. vegetable oils) and feed fat content (21% vs. 34% fat) on tissue fatty acid compositions of Atlantic salmon parr. The fish were held in fresh water under a 12 h light:12 h dark photoperiod until they doubled in body mass (from ca. 19 to 38 g, which took ca. 2 months at 8°C and ca. 6 months at 2°C), and then the muscle, viscera and carcass PLs and NLs were analysed for fatty acid composition. The ratios of unsaturated to saturated fatty acids (UFA:SFA), and the unsaturation indices (UIs, the number of unsaturated bonds per 100 fatty acid molecules) were calculated for each lipid class (PL, NL) within each tissue (muscle, viscera and carcass). Both dietary fatty acids and temperature influenced the compositions of the tissue lipids, with the dietary effects being most pronounced. The fatty acid composition of the feed oils was strongly reflected in the NLs of all three tissues, and also had a significant influence on the fatty acid profiles of the PLs. The effects of temperature were more marked in the PLs than in the NLs. Exposure to the lower temperature resulted in PLs with higher UFA:SFAs, and this is interpreted as a thermal acclimation response that would contribute to the maintenance of membrane fluidity. The PLs of fish given vegetable oils had higher UFA:SFAs than those of salmon provided with feeds containing fish oil, implying that the cell membranes of the former may have had greater fluidity. By contrast, the PLs of salmon fed with fish oil had higher concentrations of n‐3 highly unsaturated fatty acids, and higher UIs, which may have made them more prone to peroxidative damage. This raises the intriguing possibility that the feeding of vegetable oils may have produced fish that were better able to withstand exposure to low temperature as a result of improved membrane fluidity (implied from the higher UFA:SFAs in these fish), while having membrane PLs that were less susceptible to oxidative damage (implied from the lower UIs).     

Fatty acid and carotenoid composition of eggs from two nonanadromous Atlantic salmon stocks of cultured and wild origin

Two Swedish landlocked (nonanadromous) salmon (Salmo salar) stocks were investigated with the aim of characterising their egg fatty acid (FA) and carotenoid profiles. Fish from one of the stocks were also cultured over the past few decades as part of the Swedish program for genetic preservation, allowing a comparison between the eggs from females on a diet based on lipids of limnic (natural food chain) origin and eggs from females fed an artificial diet of marine origin. No significant differences in the FA profile of the phospholipid (PL) or triacylglycerol (TAG) fraction were found between the two wild stocks. The content of EPA (20:5n-3, eicosapentaenoic acid) in PL fraction was significantly higher in eggs from cultured females (13.0%) compared with eggs from both wild stocks (5.7 and 6.4%). Further, in PL fraction, AA (20:4n-6, arachidonic acid) levels in these eggs were significantly lower (2.4% versus 6.7 and 6.2%). The AA content of the TAG fraction differed greatly between wild (4.4 and 4.9%) and cultured (1.2%) eggs, whereas this fraction showed almost no corresponding difference in EPA content. The level of DHA (22:6n-3, docosahexaenoic acid) did not differ between the two wild stocks or between wild and cultured fish. This was in spite of widely different levels of DHA in the diet. The composition of carotenoids was altered in the cultured eggs which had a higher proportion and higher content (1.16 g egg^–1) of astaxanthin than the wild eggs (0.56 and 0.62 g egg^–1, respectively). Hatching success varied markedly between wild (>95%) and cultured fish (40–75%). We conclude that changes in the lipid source in the diet of female salmon during gonadal maturation will alter the egg fatty acid composition with an increased risk of disturbances in embryonic development as a consequence. Further, the lack of any difference between wild and cultured females in terms of their egg DHA content indicates that there is a strong genetic influence on levels of this fatty acid in salmon eggs.     

鱼油对幼鼠血清总脂、总胆固醇及组织脂肪酸组成的影响

本实验是选用雌雄两性的幼鼠,按随机区组法分成三组,分别在基础饲料中添加豆油、鱼油和鱼油浓缩物。喂养4周后,发现喂鱼油和鱼油浓缩物的两组幼鼠血清总脂和总胆固醇含量低于喂豆油组的(P<0.05)。脂肪酸分析表明:喂鱼油及喂鱼油浓缩物组幼鼠的脑、肝、脾和肾组织的二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)明显比喂豆油组的高。相反,喂豆油组的花生四烯酸和二十二碳四烯酸却比喂鱼油及喂鱼油浓缩物组的高。三组的体重增长率、血清总蛋白、碱性磷酸酶及脏体比都没有显著差异(P>0.05)。