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The production of farmed salmon has introduced problems regarding the quality of slaughtered fish. The contribution of collagen content to the textural properties in fish meat is studied.

Phosphatidylcholine is synthesized endogenously through the enzyme phosphatidylethanolamine-methyl transferase. As endogenous choline synthesis requires methyl groups from S-adenosylmethionine (SAM), the endogenous synthesis of choline may depend on SAM availability. SAM availability depends on methionine and ATP. SAM is also a precursor for cysteine and may affect taurine and glutathione concentrations. To investigate whether choline synthesis or transsulphuration is prioritized and the interactions between taurine and choline supplementation when methionine availability is low, juvenile Atlantic salmon were fed low methionine diets with and without taurine and choline supplementation. There were no differences in growth or protein accretion following treatments. Fish fed the low methionine diets did not develop a fatty liver, but choline supplementation increased the concentration of total phospholipids in liver and muscle. Taurine supplementation increased taurine concentrations in liver and muscle, but no interactions with choline were present. Liver SAM was unaffected by treatments. Two of three tanks fed the low methionine diet without choline and taurine supplementation had a higher gene expression of p38MAPK (mitogen activated phosphokinase). Choline supplementation to low methionine diets thus may have beneficial effect on the metabolic health and lipid transport to extra-hepatic tissues. Taurine supplementation had no effect on phospholipids status, but increased taurine concentration in tissues and as such may affect oxidation status when methionine availability is low. [ABSTRACT FROM AUTHOR]

We previously reported that juvenile Atlantic salmon with mean initial BW 11.5 g offed a methionine deficient diet had lower weight gain due to a reduced protein accretion, while lipid gain was unaffected. Muscle of the fish fed the methionine deficient diet was depleted for sulphur amino acids, while in liver, the concentration of these metabolites was maintained within narrow limits. We speculated whether this could be due to an increased muscle proteolysis to support a prioritized liver metabolism in fish fed the low methionine diets. In this study, we assessed whether genes associated with muscle proteolysis increased under methionine deficiency. The composition of the diets was similar to those used previously containing 1.6 or 2.1 g Met/16 g N. We confirmed that the fish fed the low methionine diet gained less protein compared to fish fed the DLmethionine enriched diet (P = 0.014), but growth did not reduce significantly. Also the deficient fish maintained the concentrations of liver sulphur amino acids and reduced muscle free methionine. Several of the other free amino acids within muscle increased. Further, methylation capacity was maintained in liver but reduced in the muscle (P = 0.78 and 0.04, respectively). Gene expression of muscle IGF-1 was lower (P = 0.008) and myosin light chain 2 tended (MLC2, P = 0.06) to be reduced in fish fed low methionine diet, concurrently the activity of cathepsins B+L increased (P = 0.047) in muscle of fish fed the low methionine diet. Gene expression of the muscle-specific E3 ubiquitine ligases (Murf and MaFbx) was not affected by treatment. Thus, the lower protein gain observed in fish fed the low methionine diet may be caused by reduced protein synthesis in line with the reduced IGF-1 gene expression in the white trunk muscle. Thus, to support metabolism, the dietary protein needs to be balanced in amino acids to support metabolism in all compartments of the body and secure maximal protein gain. [ABSTRACT FROM AUTHOR]

The suitability of land animal by-products (ABPs) in feed for Atlantic salmon postsmolts (initial weight 372 g) in sea water was studied in a feeding experiment, using poultry by-product meal (PBM) and porcine blood meal (BM) as protein sources and poultry oil as fat source. Four extruded feeds were tested in a 2 * 2 factorial model, with or without ABP protein sources and with or without poultry oil. The control feed contained a mix of marine and plant ingredients. Initial feed intake was highest in the ABP protein-based diets, whereas poultry oil had a weak opposite effect. No differences were seen in growth rate or body weight. Addition of PBM and BM led to increased FCR, and lower retention of crude protein and energy. This could be explained by lower digestibility of amino acids and crude protein, and a slightly lower energy level in these diets. Reduced igf1 mRNA levels in liver and muscle were seen in fish fed dietary ABP protein and oil. Despite lower protein digestibility of ABP protein, this study confirms the suitability of ABP protein and lipid in combination with plant ingredients in feed for Atlantic salmon growers. [ABSTRACT FROM AUTHOR]

The effects on Atlantic salmon ( Salmo salar L.) metabolic health of including modern processed land animal by-products ( LAP) to a plant- and marine-based diet (50% marine and 50% plant ingredients) were investigated. Three experimental diets were made with systematic replacements of both marine and plant ingredients with LAP as a source of protein (poultry meal and porcine blood meal) and fat (poultry oil) to fit a two-way factorial design. A 16-week feeding trial was performed with postsmolts in seawater (initial weight 372 g). The diet with both protein and lipids from LAP reduced liver triacylglycerols more than fourfold compared to the diet without LAP. This was confirmed by histological examinations showing reduced fatty degeneration in the liver of fish fed the high LAP diet. No severe negative effects on gut or tissue health were seen by histological examinations or by measuring genetic markers with q PCR, although a trend in the histological results indicated an improved gut health by including LAP in the diets. Clinical analyses of plasma and lipoprotein fractions showed no differences between dietary groups. [ABSTRACT FROM AUTHOR]

The current study aimed to investigate the effect of surplus dietary arginine on polyamine and amino acid metabolism and accretion of proteins and lipids, as previous studies have demonstrated a lipid-reducing effect following surplus arginine supplementation in viscera as well as increased muscle growth. Four plant protein-based diets were given increasing concentrations of L-arginine, from 21.1 to 36.1 g kg-1 DM, and fed to quadruplicate tanks of adult Atlantic salmon (1.1 kg) for 12 weeks. No effects on growth or deposition of fat or protein were observed. Free amino acid concentrations and related metabolites were unaffected in the liver, except for urea, while concentrations in muscle and plasma reflected production of arginine metabolites. Polyamine concentrations were unaffected in liver, muscle and white adipose tissue ( WAT), as were the abundance and activity of spermidine/spermine N1-acetyltransferase ( SSAT), the rate-limiting enzyme in polyamine turnover. Gene expression demonstrated differential regulation of ornithine decarboxylase ( ODC) in liver and WAT, although overall little effects were observed on gene expression. Liver S-adenosylmethionine ( SAM) concentrations decreased with arginine supplementation. We suggest that adult Atlantic salmon have adapted to surplus arginine, and the main long-term effect appears to be increased concentrations of arginine metabolites. [ABSTRACT FROM AUTHOR]

Cobia (8.4 ± 0.1 g body weight) were fed to satiation with three test diets of high plant protein-based ingredients and different lysine to arginine ratios, and one commercial diet (currently used for cobia rearing in Vietnam as a control for growth) for 6 weeks. The test diets contained 206 g marine ingredients kg−1, including fishmeal, krill meal and fish protein concentrate (in order of high to low inclusion), while the rest of the dietary protein was a blend of soya and pea protein concentrate, wheat protein and sunflower meal. Crystalline lysine and arginine were added in the test diets to produce either a balanced lysine to arginine ratio ( BL/ A; 1.1) and a high or low lysine to arginine ratio ( HL/ A; 1.8 and LL/ A; 0.8, respectively). There were no significant differences in final body weight, weight gain, feed conversion ratio or protein gain between cobia fed BL/ A- and commercial control diet ( CCT). Cobia fed BL/ A diet performed better than fish fed either HL/ A- or LL/ A diet. This was partly due to a higher feed intake and protein and lipid gain in cobia fed BL/ A diet as compared to HL/ A- and LL/ A diet. [ABSTRACT FROM AUTHOR]