Use of soy protein concentrates and lecithin products in diets fed to coho and atlantic salmon

Aquacultural production is increasing in most parts of the world, establishing new and rapidly growing markets for various oil products. One of the more interesting nutritional requirements for aquatic animals is lecithin or phosphatidylcholine. In this paper, lecithin in aquaculture is reviewed with emphasis on freshwater fish and crayfish. Further, new data on use of lecithin and two soy protein concentrates in diets fed to coho and Atlantic salmon are presented. Juvenile coho and Atlantic salmon were fed either solvent-extracted soybean meal (SBM) or Promocalf® at 30% of the diet, Promoveal® at 10, 20 or 30% of the diet, or one of three new lecithin products at a constant level of 3% of the diet. Juvenile coho salmon fed SBM, Promocalf®, or Promoveal® at 30% of the diet exhibited depressed weight gain and an elevated feed conversion ratio (FCR) compared to fish fed a positive control diet. Fish fed 10 or 20% Promoveal® had similar weight gain and FCR compared to fish fed the control diet. Coho salmon fed either of the three lecithin products (Aqualipid®, Blendmax®, or Centrol®) had similar weight gains and FCR values compared to fish fed the control diet. Whole-body proximate components were not as responsive to dietary treatments as weight gain and FCR data. Juvenile Atlantic salmon exhibited depressed weight gain only when fed 30% Promocalf® and all three lecithin products. Further, whole-body crude protein concentrations in fish fed the three lecithin products were depressed.     

The Digestibility and Accumulation of Dietary Phytosterols in Atlantic Salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) Smolt Fed Diets with Replacement Plant Oils

Phytosterols occur in high concentration in canola (Brassica napus L.) and other vegetable oils such as from the borage plant Echium (Echium plantagineum L.). We investigated if Atlantic salmon (Salmo salar) digest and accumulate dietary phytosterols in significant amounts in muscle and liver. Phytosterols are lipid soluble, lower cholesterol and reduce the risk of coronary heart disease in humans. We aimed to determine if fatty fish, such as salmon, can be used as a delivery source of this functional food component. Three diets containing canola oil (CO), Echium oil (EO) and fish oil (FO) were fed to Atlantic salmon smolt over 9 weeks. The digestibility of natural abundances of phytosterols by Atlantic salmon was poor compared to cholesterol. However, phytosterols accumulated in liver and muscle of fish. Significantly increased concentrations of 24-methylenecholesterol, campesterol, beta-sitosterol and total phytosterol occurred in livers of EO fed fish compared to FO fed fish. Campesterol concentrations increased in CO fed fish compared to the FO fed fish. We demonstrated that natural abundances of dietary phytosterols are digested by and accumulated in liver and white muscle of Atlantic salmon smolt. However, phytosterol levels in salmon muscle will not be a major source of phytosterols in human diets and would not be expected to significantly effect human cardiovascular health.     

Uncoupling EPA and DHA in Fish Nutrition: Dietary Demand is Limited in Atlantic Salmon and Effectively Met by DHA Alone

Due to the scarcity of marine fish oil resources, the aquaculture industry is developing more efficient strategies for the utilization of dietary omega‐3 long‐chain polyunsaturated fatty acids (n‐3 LC‐PUFA). A better understanding of how fish utilize EPA and DHA, typically provided by fish oil, is needed. However, EPA and DHA have different physiological functions, may be metabolized and incorporated into tissues differently, and may vary in terms of their importance in meeting the fatty acid requirements of fish. To address these questions, Atlantic salmon were fed experimental diets containing, as the sole added dietary lipid source, fish oil (positive control), tallow (negative control), or tallow supplemented with EPA, DHA, or both fatty acids to ~50 or 100 % of their respective levels in the positive control diet. Following 14 weeks of feeding, the negative control diet yielded optimum growth performance. Though surprising, these results support the notion that Atlantic salmon requirements for n‐3 LC‐PUFA are quite low. EPA was largely β‐oxidized and inefficiently deposited in tissues, and increasing dietary levels were associated with potential negative effects on growth. Conversely, DHA was completely spared from catabolism and very efficiently deposited into flesh. EPA bioconversion to DHA was largely influenced by substrate availability, with the presence of preformed DHA having little inhibitory effect. These results clearly indicate EPA and DHA are metabolized differently by Atlantic salmon, and suggest that the n‐3 LC‐PUFA dietary requirements of Atlantic salmon may be lower than reported and different, if originating primarily from EPA or DHA.     

β-oxidation capacity of red and white muscle and liver in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.)—Effects of increasing dietary rapeseed oil and olive oil to replace capelin oil

Post-smolt Atlantic salmon (Salmo salar) were fed six diets in which capelin oil was replaced with 0, 25, 50, 75, or 100% rapeseed oil (RO; low-erucic acid) or 50% olive oil (OO). The experimental diets were fed to single groups of Atlantic salmon for 42 wk, whereas the 100% capelin oil (0% RO) diet was fed in duplicate. The β-oxidation capacity of palmitoyl-CoA was determined, using a method optimized for salmon tissues, at the start of the experiment, after 21 wk (October), and after 42 wk (March) in red and white muscle and in liver. Red muscle showed the highest specific β-oxidation capacity, but when expressed as total β-oxidation capacity for the whole tissue, white muscle was the most important tissue for the β-oxidation of FA. From the initial to the final sampling, the β-oxidation capacity of white muscle increased significantly, whereas the β-oxidation capacity in liver decreased significantly. After 22 wk, white muscle exhibited an increased β-oxidation capacity when the dietary RO content was raised from 25 to 75%, with similar effects in red muscle and liver after 42 wk of feeding. The present results also show that the β-oxidation capacity increased with an increase in fish size.     

Modification of membrane fatty acid composition,eicosanoid production,and phospholipase a activity in Atlantic Salmon (Salmo salar) gill and kidney by dietary lipid

Atlantic salmon post-smolts were fed diets containing either fish oils (Fosol, FO and Marinol, MO) rich in long-chain n-3 polyunsaturated fatty acids (PUFA), or plant oils rich in 18:2n-6 (sunflower oil, SO) or 18:3n-3 (linseed oil, LO) for 12 wk. The major PUFA in individual phospholipids from gill and kidney were related to the dietary lipid intake. Levels of n-6 PUFA were highest while levels of n-3 PUFA were lowest in fish fed SO. Fish fed LO generally had lower levels of 20:4n-6 compared to the other treatments while fish fed SO generally had the highest levels of 20:4n-6. In all phospholipid classes except phosphatidylinositol (PI) 20:5n-3 was greatest in fish fed MO followed by FO, LO, and SO. In PI, 20:5n-3 was also highest in fish fed MO but those fed LO contained more 20:5n-3 than those fed FO. This resulted in the ratio of the eicosanoid precursors, 20:4n-6/20:5n-3, being significantly greater in fish fed SO, for all phospholipid classes, compared to fish fed the other three dietary oils. The activity of gill phospholipase A was greatest in fish fed FO and was lowest in fish fed SO. The concentration of PGF_3α was significantly increased in gill homogenates from fish fed MO compared to the other three treatments while PGF_2α was significantly increased in fish fed SO compared to those fed LO. The concentration of PGE₃ was significantly reduced in kidney homogenates from fish fed SO compared to the other three treatments while PGE₂ was significantly increased in fish fed SO compared to those fed either FO or LO.     

Dietary n-3 HUFA Affects Mitochondrial Fatty Acid β-Oxidation Capacity and Susceptibility to Oxidative Stress in Atlantic Salmon

Atlantic salmon (Salmo salar) (90 g) were fed four different diets for 21 weeks (final weight 344 g). The levels of n-3 highly unsaturated fatty acids (HUFA) ranged from 11% of the total fatty acids (FA) in the low n-3 diet to 21% in the intermediate n-3 diet, to 55 and 58% in the high n-3 diets. The high n-3 diets were enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA). Increasing dietary levels of n-3 HUFA led to increasing percentages (from 31 to 52%) of these FA in liver lipids. The group fed the highest level of DHA had higher expressions of peroxisome proliferator-activated receptor (PPAR) β and the FA β-oxidation genes acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase (CPT)-II, compared to the low n-3 groups. The high n-3 groups had reduced activity of mitochondrial cytochrome c oxidase and β-oxidation capacity, together with increased activities of superoxide dismutase (SOD) and caspase-3 activities. In the group fed the highest level of n-3 HUFA, decreased percentages of major phospholipids (PL) in the mitochondrial and microsomal membranes of the liver were also apparent. The percentage of mitochondrial cardiolipin (Ptd₂Gro) was 3.1 in the highest n-3 group compared to 6.6 in the intermediate group. These data clearly show an increased incidence of oxidative stress in the liver of fish fed the high n-3 diets.     

The effect of dietary lipid on polyunsaturated fatty acid metabolism in Atlantic salmon (Salmo salar) undergoing parr-smolt transformation

The aim of this study was to measure the changes in lipid metabolism which occur during smoltification and seawater transfer in Atlantic salmon (Salmo salar). Duplicate groups of Atlantic salmon parr were fed diets containing either fish oil (FO) or a blend of linseed and rapeseed oils, vegetable oil (VO), from October (week 0) to seawater transfer in May (week 26). From May to August (weeks 26–43), all fish were fed a fish oil-containing diet. Fatty acyl desaturation and elongation activity were followed in isolated hepatocytes incubated with radioactive 18:3n−3 and 18:2n−6. Metabolism of 18:3n−3 was consistently around 5-fold greater than metabolism of 18:2n−6, and total metabolism of both substrate polyunsaturated fatty acids (PUFA) was increased in fish fed both VO and FO up to seawater transfer after which desaturation activities were reduced. Desaturation activities with both 18:3n−3 and 18:2n−6 were significantly greater in fish fed VO, compared to fish fed FO, at 22 and 26 wk. Arachidonic acid (20:4n−6; AA) in liver polar lipids (PL) of fish fed VO increased consistently from weeks 0–22 but varied after seawater transfer. In fish fed FO, AA in liver PL remained constant up to week 17 before increasing at seawater transfer and leveling off thereafter. Eicosapentaenoic acid (20:5n−3; EPA) in liver PL of fish fed VO decreased significantly from week 0–22 before rising at seawater transfer and increasing rapidly posttransfer. EPA in liver PL of fish fed FO showed a similar trend except EPA was always greater in the freshwater phase compared to fish fed VO. Docosahexaenoic acid (DHA) levels in liver PL of fish fed VO remained constant in the freshwater phase before increasing following seawater transfer. In fish fed FO, DHA in liver PL increased from weeks 0–17 reducing and leveling off postseawater transfer. The levels of PGF_2α and PGF_3α were measured in isolated gill cells stimulated with calcium ionophore A23187. PGF_2α production in fish fed VO increased significantly between 0–7 wk before decreasing toward seawater transfer. After transfer, PGF_2α production increased to a peak at 35 wk. PGF_2α production in fish fed FO was not significantly altered during the trial period. The changes in PGF_3α production were broadly similar to those occurring with PGF_2α, but the latter was always in excess of the former (2-to 4-fold). Plasma chloride concentrations in fish subjected to seawater challenge at 20 wk were significantly lower in fish fed VO compared to those fed FO. This study has provided new information on the changes in lipid metabolism which accompany parr-smolt transformation and suggests that diets which have a fatty acid composition more similar to that in aquatic invertebrates may be beneficial in effecting successful seawater adaptation.     

Fucosterol Causes Small Changes in Lipid Storage and Brassicasterol Affects some Markers of Lipid Metabolism in Atlantic Salmon Hepatocytes

Several feeding trials with Atlantic salmon fed naturally high phytosterol concentrations due to dietary rapeseed oil inclusion have shown changes in lipid metabolism and increased hepatic lipid storage in the fish. An in vitro trial with Atlantic salmon hepatocytes was, therefore, performed to study the possible direct effects of phytosterols on lipid storage and metabolism. The isolated hepatocytes were exposed to seven different sterol treatments and gene expression, as well as lipid accumulation by Oil Red O dyeing, was assessed. Fucosterol, a sterol found in many algae species, had an effect on the size of individual lipid droplets, leading to smaller lipid droplets than in the control without added sterols. A sterol extract from soybean/rapeseed led to an increase in the percentage of hepatocytes with visible lipid droplets at 20× magnification, while hepatocytes of both the sterol extract‐treated groups and fucosterol‐treated groups had a larger proportion of their area covered with lipids compared to control cells. Brassicasterol, a sterol characteristic of rapeseed oil, was the only sterol treatment leading to a change in gene expression, affecting the expression of the nuclear receptors, peroxisome proliferator‐activated receptor gamma (pparg) and retinoid X receptor (rxr). The current study thus shows that phytosterols can have direct, although subtle, effects on both hepatic lipid storage and gene expression of Atlantic salmon in vitro.     

The effect of enhanced intake of linoleic acid on the fatty acid composition of tissue polar lipids of post-smolt atlantic salmon (Salmo salar)

Duplicate groups of Atlantic salmon (Salmo salar) post smolts were given diets in which the lipid component was either fish oil or a mixture of corn oil and lard. This difference in the dietary lipid did not significantly affect growth over a period of sixteen weeks. Proportions of docosahexaenoic acid [22∶6(n−3)] and total (n−3) fatty acids in the polar lipids of liver and white muscle were unaffected by this difference in dietary lipid component over the time period used. Fish given the diet containing corn oil and lard had significantly higher levels of 20∶2(n−6), 20∶3(n−6) and 20∶4(n−6) in the polar lipids of these tissues than were present in the tissues of the fish given diets containing fish oil. There results suggest that linoleic acid [18∶2(n−6)] undergoes elongation and desaturation to arachidonic acid [20∶4(n−6)] in post-smolt Atlantic salmon.     

Influence of holding time on the interfacial solid solution and mechanical properties of agglomerated white fused alumina abrasives

In this paper, the aging relationship between holding time and the interfacial solid solution was utilized to prepare high-performance agglomerated white fused alumina (AWA) abrasives. The influence of holding time on the interfacial solid solution and mechanical properties of AWA abrasives were systematically investigated, and the grinding performance was thoroughly analyzed. The results showed that increasing the holding time caused the Al₂O₃ to violently infiltrate the interface between the white fused alumina (WA) particles and the vitrified bond, which led to the precipitation of a large amount of β-spodumene and monoclinic celsian in the vitrified bond and transformed the simple mechanical bonds between the WA particles and the vitrified bond into stronger chemical bonds. Thus, it was possible to control the mechanical properties of the AWA abrasives by adjusting the holding time. Specifically, after sintering at 760 °C for 4h, the single particle compressive strength and impact toughness reached the maximum values of 26 N and 63%, respectively. In comparison with the WA grinding wheel, the grinding ratio of the AWA grinding wheel was increased by 17.9% and the workpiece surface roughness was reduced by 21.1%.     

Highly unsaturated fatty acid synthesis in vertebrates: New insights with the cloning and characterization of a Δ6 desaturase of Atlantic salmon

Fish are an important source of the n−3 highly unsaturated fatty acids (HUFA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids that are crucial to the health of higher vertebrates. The synthesis of HUFA involves enzyme-mediated desaturation, and a Δ5 fatty acyl desaturase cDNA has been cloned from Atlantic salmon (Salmo salar) and functionally characterization of a Δ6 fatty acyl desaturase of Atlantic salmon and describe its genomic structure, tissue expression, and nutritional regulation. A salmon genomic library was screened with a salmon Δ5 desaturase cDNA and positive recombinant phage isolated and subcloned. The full-length cDNA for the putative fatty acyl desaturase was shown to comprise 2106 bp containing an open reading frame of 1365 bp specifying a protein of 454 amino acids (GenBank accession no. AY458652). The protein sequence included three histidine boxes, two transmembrane regions, and an N-terminal cytochrome b₅ domain containing the heme-binding motif HPGG, all of which are characteristic of microsomal fatty acid desaturases. Functional expression showed that this gene possessed predominantly Δ6 desaturase activity. Screening and sequence analysis of the genomic DNA of a single fish revealed that the Δ6 desaturase gene constituted 13 exons in 7965 bp of genomic DNA. Quantitative real-time PCR assay of gene expression in Atlantic salmon showed that both Δ6 and Δ5 fatty acyl desaturase genes, and a fatty acyl elongase gene, were highly expressed in intestine, liver, and brain, and less so in kidney, heart, gill, adipose tissue, muscle, and spleen. Furthermore, expression of both Δ6 and Δ5 fatty acyl desaturase genes in intestine, liver, red muscle, and adipose tissue was higher in salmon fed a diet containing vegetable oil than in fish fed a diet containing fish oil.     

Fatty acyl desaturation in isolated hepatocytes from Atlantic salmon (Salmo salar): Stimulation by dietary borage oil containing γ-linolenic acid

The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation of [1-¹⁴C]18∶3n−3 and [1-¹⁴C]18∶2n−6 were investigated in isolated hepatocytes from Atlantic salmon. Atlantic salmon smolts were fed diets containing either a standard fish oil (FO) as a control diet, a 1∶1 blend of Southern Hemisphere marine oil and tuna orbital oil (MO/TO), sunflower oil (SO), borage oil (BO), or oliver oil (OO) for 12 wk. The SO and BO diets significantly increased the percentages of 18:2n−6, 18:3n−6, 20:2n−6, 20:3n−6, and total n-6 polyunsaturated fatty acids (PUFA) in salmon liver lipids in comparison with the FO diet. The BO diet also increased the percentage of 20:4n−6. Both the SO and BO diets significantly reduced the percentages of all n−3 PUFA in comparison with the FO diet. The OO diet significantly increased the percentages of 18:1n−9, 18:2n−6, total monoenes, and total n−6 PUFA in liver lipids compared to the FO diet, and the percentages of all n−3 PUFA were significantly reduced. With [1-¹⁴C]18:3n−3, the recovery of radioactivity in the products of Δ6 desaturation was significantly greater in the hepatocytes from salmon fed SO, BO, and OO in comparison with the FO diet. The BO diet also increased the recovery of radioactivity in the products of Δ5 desaturation. Only the BO diet significantly affected the desaturation of [1-¹⁴C]18:2n−6, increasing recovery of radioactivity in both Δ6- and Δ5-desaturation products. In conclusion, dietary BO, enriched in γ-linolenic acid (18:3n−6), significantly increased the proportions of both 20:3n−6 and 20:4n−6 in salmon liver phospholipids and also significantly increased the desaturation of both 18:2n−6 and 18:3n−3 in salmon hepatocytes. The possible relationships between dietary fatty acid composition, tissue phospholipid fatty acid composition, and desaturation/elongation activities are discussed.     

Effect of diets rich in linoleic or α-linolenic acid on phospholipid fatty acid composition and eicosanoid production in atlantic salmon (Salmo salar)

Atlantic salmon post-smolts were fed diets rich in linoleic acid (sunflower oil, SO), α-linolenic acid (linseed oil, LO) or long-chain polyunsaturated fatty acids (fish oil, FO) for a period of 12 wk. In the liver phospholipids of fish fed SO, the levels of 18∶2n−6, 20∶2n−6, 20∶3n−6 and 20∶4n−6 were significantly elevated compared to both other treatment. In choline phospholipids (CPL), ethanolamine phospholipids (EPL) and phosphatidylserine (PS) the levels of 22∶4n−6 and 22∶5n−6 were significantly elevated in fish fed SO. In liver phospholipids from fish fed LO, 18∶2n−6, 20∶2n−6 and 20∶3n−6 were significantly elevated but 20∶4n−6, 22∶4n−6 and 22∶5n−6 were similar or significantly decreased compared to fish fed FO. Liver phospholipids from fish fed LO had increased 18∶3n−3 and 20∶4n−3 compared to both other treatments while EPL and phosphatidylinositol (PI) also had increased 20∶5n−3. In fish fed LO, 22∶6n−3 was significantly reduced in CPL, PS and PI compared to fish fed FO. Broadly similar changes occurred in gill phospholipids. Production of 12-lipoxygenase metabolites in isolated gill cells stimulated with the Ca²⁺-ionophore A23187 were significantly reduced in fish fed either SO or LO compared to those fed FO. However, the ratio 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE)/12-hydroxy-5,8,10,14,17-eicosapentaenoic acid (12-HEPE) was significantly elevated in stimulated gill cells from SO-fed fish. Although mean values of thromboxane B₂ (TXB₂) and prostaglandin E₂ (PGE₂) were increased in fish fed SO, they were not significantly different from those of the other two treatments.     

Lipid metabolism and tissue composition in Atlantic salmon (Salmo salar L.)—Effects of capelin oil, palm oil, and oleic acid-enriched sunflower oil as dietary lipid sources

Triplicate groups of Atlantic salmon (Salmo salar L.) were fed four diets containing different oils as the sole lipid source, i.e., capelin oil, oleic acid-enriched sunflower oil, a 1∶1 (w/w) mixture of capelin oil and oleic acid-enriched sunflower oil, and palm oil (PO). The β-oxidation capacity, protein utilization, digestibility of dietary fatty acids and fatty acid composition of lipoproteins, plasma, liver, belly flap, red and white muscle were measured. Further, the lipid class and protein levels in the lipoproteins were analyzed. The different dietary fatty acid compositions did not significantly affect protein utilization or β-oxidation capacity in red muscle. The levels of total cholesterol, triacylglycerols, and protein in very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL), and plasma were not significantly affected by the dietary fatty acids. VLDL, LDL, and HDL fatty acid compositions were decreasingly affected by dietary fatty acid composition. Dietary fatty acid composition significantly affected both the relative fatty acid composition and the amount of fatty acids (mg fatty acid per g tissue, wet weight) in belly flap, liver, red and white muscle. Apparent digestibility of the fatty acids measured by adding yttrium oxide as inert marker, was significantly lower in fish fed the PO diet compared to the other three diets.     

Effects of dietary corn oil and salmon oil on lipids and prostaglandin E2 in rat gastric mucosa

Three groups of male rats were fed either a corn oilenriched diet (17%, w/w), a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) or a low-fat diet (4.4%) for eight wk to investigate the possible relationships between dietary fatty acids and lipid composition, and prostaglandin E₂ level and phospholipase A₂ activity in the rat gastric mucosa. High-fat diets induced no important variation in total protein, phospholipid and cholesterol contents of gastric mucosa. Compared with a low-fat diet, corn oil produced a higher n−6/n−3 ratio in mucosal lipids, whereas this ratio was markedly lowered by a fish oil diet. In comparison with the low-fat diet, the production of prostaglandin E₂(PGE₂) in gastric mucosa of rats fed salmon oil was significantly, decreased by a factor of 2.8. In the corn oil group, PGE₂ production tended to decrease, but not significantly. In comparison with the low-fat diet, both specific and total gastric mucosal phospholipase A₂ activities were increased (+18 and 23%, respectively) in the salmon oil group; they were unchanged in the corn oil group. It is suggested that the decrease of gastric PGE₂ in rats fed fish oil is not provoked by a decrease in phospholipase A₂ activity but may be the result of the substitution of arachidonic acid by n−3 PUFA or activation of PGE₂ catabolism.     

Atlantic Salmon Mucins Inhibit LuxS-Dependent A. Salmonicida AI-2 Quorum Sensing in an N-Acetylneuraminic Acid-Dependent Manner

One of the most important bacterial diseases in salmonid aquaculture is furunculosis, caused by Aeromonas salmonicida. Bacterial communication through secreted autoinducer signals, quorum sensing, takes part in the regulation of gene expression in bacteria, influencing growth and virulence. The skin and mucosal surfaces, covered by a mucus layer, are the first point of contact between fish and bacteria. Mucins are highly glycosylated and are the main components of mucus. Here, we validate the Vibrio harveyi BB170 bioreporter assay for quantifying A. salmonicida quorum sensing and study the effects of Atlantic salmon mucins as well as mono- and disaccharides on the AI-2 levels of A. salmonicida. Atlantic salmon mucins from skin, pyloric ceca, proximal and distal intestine reduced A. salmonicida AI-2 levels. Among the saccharides abundant on mucins, fucose, N-acetylneuraminic acid and GlcNAcβ1-3Gal inhibited AI-2 A. salmonicida secretion. Removal of N-acetylneuraminic acid, which is the most abundant terminal residue on mucin glycans on Atlantic salmon mucins, attenuated the inhibitory effects on AI-2 levels of A. salmonicida. Deletion of A. salmonicida luxS abolished AI-2 production. In conclusion, Atlantic salmon mucins regulate A. salmonicida quorum sensing in a luxS and N-acetylneuraminic acid-dependent manner.     

Regiospecificity profiles of storage and membrane lipids from the gill and muscle tissue of atlantic salmon (Salmo salar L.) grown at elevated temperature

Regiospecific and traditional analysis, of both storage and membrane lipids, was performed on gill, white muscle, and red muscle samples taken from Atlantic salmon (Salmo salar) to gauge the effect of elevated water temperature. The fish, fed a commercial diet, were held at an elevated water temperature of 19°C. Total n-3 PUFA, total PUFA, and n-3/n-6 and unsaturated/saturated fatty acid (UFA/SFA) ratios in the FA profile of the total lipid extract in the white muscle were fairly low compared with fish grown at 15°C. Adaptation of structural and storage lipids at elevated temperatures was shown by a significant (P<0.01) reduction in PUFA especially in the percentage of EPA (6–8%). Further adaptation was indicated by the percentages of SFA, which were significantly (P<0.05) higher in gill (56%) and white muscle (58%) polar lipid fractions and coincided with lower percentages of n-3, n-6, and total PUFA. The regiospecific profiles indicated a high affinity of DHA to the sn-2 position in both the TAG (61–68%) and polar lipid (35–60%) fractions. The combination of detailed regiospecific and lipid analyses demonstrated adaptation of cell membrane structure in Atlantic salmon grown at an elevated water temperature.     

Effects of fish oil,corn oil and lard diets on lipid peroxidation status and glutathione peroxidase activities in rat heart

In this study, we investigated the effect of various types of fats on heart lipid peroxidation status and on blood lipid parameters. Rats were fed either a low-fat diet (2.2% lard plus 2.2% corn oil), a corn oil diet (17%), a salmon oil diet (12.5%) supplemented with 4.5% corn oil, or a lard diet (15%) supplemented with 2% corn oil. All diets were supplemented with 1% cholesterol. Rats were fed for eight weeks. When compared with the low-fat diet, the salmon oil-diet intake resulted in a lower blood cholesterol, triglyceride and phospholipid concentrations (−50, −56 and −30%, respectively). Corn oil only tended to lower blood lipids; this decrease was significant for triglycerides only (−40%). The hypocholesterolemic effect of salmon oil diet is even more pronounced, if blood cholesterol values are compared with those of rats fed the lard diet. Heart lipid composition was not affected by dietary manipulations. Fatty acid composition of cardiac phosphatidylcholines and phosphatidylethanolamines, however, were altered by high-fat diets. In phosphatidylcholine, salmon oil induced a twelvefold decrease in the n−6/n−3 ratio and a 26% increase in the unsaturation index. For phosphatidylethanolamine, the n−6/n−3 ratio decreased 7.7-fold and the unsaturation index increased by 13%. A 50% decrease of the n−6/n−3 ratio was observed in animals fed the lard diet. Ultramicroscopic examination of ventricles revealed that those of the salmon oil group significantly accumulated lipofuscin-like or ceroid material, whereas this accumulation was barely detectable in hearts of the other groups. Seleniumdependent glutathione peroxidase activity tended to be the highest in hearts of rats fed the salmon oil diet; this increase is significant (+36% and +54% for total and specific activities, respectively), if values are compared with those of the rats fed the lard diet. Liver glutathione peroxidase and heart glutathione S-transferases activities remained unchanged. These results indicate that fish oil did not lower the selenium involved in glutathione peroxidase activity. This rules out that a deficiency in this enzyme was at the origin of heart lipofuscinosis. Also, it is concluded that the n−6/n−3 ratio of the diet is likely more determinant in the alteration of heart lipid peroxidation status than is the polyunsaturated/saturated ratio. Part of this work was presented at the International Congress: “Selenium in Medicine and Biology,” Avoriaz, France, March, 15–18, 1988.     

FA composition of the oil extracted from farmed atlantic salmon (Salmo salar L.) viscera

The FA composition of visceral oil extracted from farmed Atlantic salmon (Salmo salar L.) viscera was studied. Seventeen FA were identified in the extracted visceral oil, and the major FA were 18∶1n9, 16∶0, 16∶1n7, 20∶5n3 (EPA), 14∶0, and 22∶6n3 (DHA). The percentages of saturated, monounsaturated, and polyunsaturated FA in the total FA were 31.7, 36.0, and 32.2%, respectively. Compared with other fish oils, oil from farmed Atlantic salmon had much higher EPA (1.64 g/100 g) and DHA (1.47 g/100 g) contents. The FA profile of the salmon visceral oil was similar to that of the salmon fillet. Thus, the salmon visceral oil could be a replacement for the oil obtained from edible salmon fillet and used in functional foods or feeds requiring a high level of omega-3 FA. Furthermore, producing visceral oil is also beneficial to salmon fish industry by adding value back to the processing waste.