Farmed salmon feeds have changed from purely marine-based diets with high levels of EPA and DHA in the 1990s to the current 70 % plant-based diets with low levels of these fatty acids (FA). The aim of this study was to establish the impacts of low dietary EPA and DHA levels on performance and tissue integrity of Atlantic salmon (Salmo salar). Atlantic salmon (50 g) in seawater were fed fourteen experimental diets, containing five levels (0, 0·5, 1·0, 1·5 and 2·0 %) of EPA, DHA or a 1:1 EPA + DHA plus control close to a commercial diet, to a final weight of 400 g. Lack of EPA and DHA did not influence mortality, but the n-3-deficient group exhibited moderately slower growth than those fed levels above 0·5 %. The heart and brain conserved EPA and DHA levels better than skeletal muscle, liver, skin and intestine. Decreased EPA and DHA favoured deposition of pro-inflammatory 20 : 4n-6 and 20 : 3n-6 FA in membrane phospholipids in all tissues. When DHA was excluded from diets, 18 : 3n-3 and EPA were to a large extent converted to DHA. Liver, skeletal and cardiac muscle morphology was normal in all groups, with the exception of cytoplasm packed with large or foamy vacuoles and sometimes swollen enterocytes of intestine in both deficient and EPA groups. DHA supplementation supported normal intestinal structure, and 2·0 % EPA + DHA alleviated deficiency symptoms. Thus, EPA and DHA dietary requirements cannot be based exclusively on growth; tissue integrity and fish health also need to be considered.Key words: Aquafeed: DHA: EPA: Essential fatty acids: Fat: Phospholipids Continued growth of the Atlantic salmon (Salmo salar) farming industry depends on the availability of sustainable feed ingredients in the world market. For optimal use of ingredients with limited availability, information regarding nutritional requirements is of utmost importance. Fatty acid (FA) composition of salmon diets has changed considerably over the last several decades. Although 90 % of traditional Norwegian salmon diets were composed of marine ingredients in the 1990s, current diets only contain approximately 30 % marine ingredients (1)

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Microalgae, as primary producers of EPA and DHA, are among the most prominent alternative sources to fish oil for n-3 long-chain PUFA in animal and human nutrition. The present study aimed to assess technical, nutritional and fish health aspects of producing n-3-rich Atlantic salmon (Salmo salar) fish fillets by dietary supplementation of increasing levels of a DHA-producing Schizochytrium sp. and reduced or without use of supplemental fish oil. Atlantic salmon smolt were fed diets with graded levels of microalgae for 12 weeks, during which all fish showed high feed intake rates with postprandial plasma leptin levels inversely correlating with final mean fish body weights. Fish performance was optimal in all experimental treatments (thermal growth coefficient about 4·0 and feed conversion ratio 0·8–0·9), protein digestibility was equal in all diets, whereas dietary lipid digestibility inversely correlated with the dietary levels of the SFA 16 : 0. Fillet quality was good and similar to the control in all treatments in terms of n-3 long-chain PUFA content, gaping, texture and liquid losses during thawing. Histological fluorescence staining and immunofluorescence analysis of salmon intestines (midgut: base of intestine and villi) revealed significant effects on slime, goblet cell production and inducible nitric oxide synthase (iNOS) activity with increasing levels of dietary Schizochytrium sp. supplementation. Microarray analysis did not reveal any signs of toxicity, stress, inflammation or any other negative effects from Schizochytrium sp. supplementation in diets for Atlantic salmon.

The present study aimed to determine the minimum requirements of the essential n-3 fatty acids EPA and DHA in Atlantic salmon (Salmo salar) that can secure their health under challenging conditions in sea cages. Individually tagged Atlantic salmon were fed 2, 10 and 17 g/kg of EPA + DHA from 400 g until slaughter size (about 3·5 kg). The experimental fish reared in sea cages were subjected to the challenging conditions typically experienced under commercial production. Salmon receiving the lowest EPA + DHA levels showed lower growth rates in the earlier life stages, but no significant difference in final weights at slaughter. The fatty acid composition of various tissues and organs had remarkably changed. The decreased EPA + DHA in the different tissue membrane phospholipids were typically replaced by pro-inflammatory n-6 fatty acids, most markedly in the skin. The EPA + DHA levels were maintained at a higher level in the liver and erythrocytes than in the muscle, intestine and skin. After delousing at high water temperatures, the mortality rates were 63, 52 and 16 % in the salmon fed 2, 10 and 17 g/kg EPA + DHA. Low EPA + DHA levels also increased the liver, intestinal and visceral fat amount, reduced intervertebral space and caused mid-intestinal hyper-vacuolisation. Thus, 10 g/kg EPA + DHA in the Atlantic salmon diet, a level previously regarded as sufficient, was found to be too low to maintain fish health under demanding environmental conditions in sea cages.

Two myostatin isoforms were identified in Atlantic salmon (Salmo salar) by RT‐PCR, and genomic sequences encoding this negative muscle growth factor were for the first time isolated from a nonmammalian species. Salmon myostatin isoform I is transcribed in white skeletal muscle as a 2346‐nucleotide mRNA species that encodes a precursor protein of 373 amino acids. Salmon myostatin I shows 93% sequence identity with isoform II which was isolated from white muscle as a partial cDNA sequence of 1409 nucleotides. In contrast to the restricted gene expression of myostatin in mammals, salmon myostatin I and II mRNAs were identified by RT‐PCR in multiple tissues, including white muscle, intestine, brain, gills, tongue and eye. In addition, isoform I mRNA was found in red skeletal muscle, heart, spleen, and ovarian tissue. Using polyclonal antibodies against both isoforms, a 55‐kDa precursor protein was detected by Western blot analysis in the red and white skeletal muscle, heart, intestine, and brain. Immunoreactive peptides of 35–40 kDa were identified in the gills, tongue, spleen, and head kidney, while the 25‐kDa mature myostatin was found in the eye and serum, and in vitro expressed in rabbit reticulocyte lysate. Salmon myostatin was immunohistochemically localized in the sarcoplasma of red and white muscle fibres, in intestinal epithelial cells, at the basis of the branchial primary lamellae, and in odontoblasts and ameloblasts of the tongue teeth. The results indicate that the role of fish myostatin may not be restricted to muscle growth regulation, but may have additional functions similar to the growth/differentiation factor‐11 in mammals.

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IntroductionFemale patients (n = 20) with osteoporosis, aged 66±5 yr were studied during a 24-h infusion of parathyroid hormone at a rate of 0.5 IU equivalents/kg* h, and then during a 28-d period of subcutaneous injections, at a dose of 800 IU equivalents per day. Thereafter halfthe patients received subcutaneous injections of calcitonin, 75 U/d for 42 d, and all patients were followed to the end of a 90-d cycle. Biochemical markers of bone formation (serum alkaline phosphatase, osteocalcin, and the carboxy-terminal extension peptide of procollagen 1 ) and bone resorption (fasting urine calcium, hydroxyproline, and deoxypyridinoline) were compared during treatment by the intravenous and subcutaneous route of PTH administration, and subsequently during calcitonin therapy. During intravenous PTH infusion there were significant reductions in all three bone formation markers, despite expected rises in urinary calcium and hydroxyproline. By contrast, the circulating markers of bone formation increased rapidly by > 100% of baseline values during daily PTH injections (P <0.001). Significant increases in bone resorption markers were only seen at the end of the 28 d of injections, but were < 100% over baseline values, (P < 0.05). Quantitative bone histomorphometry from biopsies obtained after 28 d of PTH treatment confirmed that bone formation at both the cellular and tissue levels were two to five times higher than similar indices measured in a control group of biopsies from untreated osteoporotic women. Subsequent treatment of these patients with calcitonin showed no significant changes in the biochemical markers of bone formation and only a modest attenuation of bone resorption.Thus, PTH infusion may inhibit bone formation, as judged by circulating biochemical markers, whereas daily injections confirm the potent anabolic actions of the hormone. Sequential calcitonin therapy does not appear to act synergistically with PTH in cyclical therapeutic protocols. (J.

In vitro cultivated Atlantic salmon (Salmo salar L.), hepatocytes were incubated without or with a mixture of sesamin and episesamin in order to test for possible effects on lipid metabolism. Sesamin/episesamin exposure (0.05 mM, final concentration) led to increased elongation and desaturation of (14)C 18:3n-3 to docosahexaenoic acid ((14)C 22:6n-3, DHA, P < 0.01) and down regulated gene expression of Delta6 and Delta5 desaturases compared to control treatment. Sesamin/episesamin further increased the hepatocytes capacity for fatty acid beta-oxidation of (14)C 18:3n-3 (P < 0.01) to the (14)C acid soluble products, acetate, malate and oxaloacetate, in agreement with an increased gene expression of carnitine palmitoyltransferase I. Also the gene expression of cluster of differentiation 36 was upregulated and the expression of scavenger receptor type B, peroxisome proliferator-activated receptors alpha and gamma were downregulated. The amount of triacylglycerols secreted by the cells tended to be lower in the sesamin/episesamin incubated hepatocytes than the control cells. This study shows that sesamin has favourable effects on lipid metabolism leading to increased level of DHA, which may be of interest for aquaculture use.