Influence of nutritional factors on muscle development and texture of Atlantic salmon ( Salmo salar L.). In vivo and in vitro studies.

The aim of the present study was to examine the effect of amino acids or bioactive fatty acid on the Atlantic salmon flesh quality with main emphasis on the muscle development and filletstexture by in vivo and in vitro strategies. For the in vivo study, the fish were fed a commercial extruded dry feed i.e. control (Con) diet or the same diet supplemented with tetradecylthioacetic acid (TTA), arginine (Arg) or glutamate (Glu) for a period of five months. A total of 12 net-pens with triplicate randomly assigned net pens of each diet were setup. A total of 108 salmon (nine fish per net-pen) were used, whereof two subgroups were made according to pre-slaughter handling: non-crowded, NC (harvested using normal procedure, n=72) and crowded, C (exposed to crowding stress for 16 hours before slaughter, n=36). Parameters studies included fillet contraction, muscle pH, texture, cathepsin B, L and cathepsin B+L, and histological analysis. For the in vitro study, fifty Atlantic salmon parr with an average length of 5-7cm were used for isolation of myosatellite cells. Three experimental treatments, arginine (Arg), glutamine (Gln) and tetradecylthioacetic acid (TTA), in addition to one control (Con) treatment were made and supplemented to the isolated myosatellite cells that were incubated at two different temperatures, either 8°C (10 days) or 16°C (7 days) for PCNA and qPCR analysis. In the PCNA assay, proliferation percentage of blue and brown cells nuclei was performed. In qPCR study, two muscle genes, myogenin (regulatory) and myosin light chain 2 (structural) were selected, and in addition also two genes for the proteases cathepsin B and cathepsin L. In the in vivo study, Arg and TTA diets in NC group and only Arg diet in C group showed a tendency towards lowering the fillet contraction. Muscle pH was significantly increased by Glu diet in C group but unfortunately, pH was significantly lowered by Arg and TTA in NC group. Moreover, Arg and Glu diets showed more firm fillet texture in both NC and C groups whereas TTA diet had only in C group. Data from histology revealed higher tendencies by Arg and Glu dietsin increasing the cell numbers of NC and C groups respectively, whereas significantly lower tendency by TTA diet in NC group and vice versa. Further, analysis of cathepsins showed that only the activity of cathepsin B is influenced by the Arg, Glu and TTA diets. Pre-slaughter crowding stress demonstrated significantly negative effect on fillet contraction, muscle pH, as well as the texture. In the in vitro study, results from PCNA indicated higher proliferation of muscle cells by Arg and Gln treatments at 8°C and 16°C respectively, whereas a significantly lower proliferation byTTA treatment at both temperatures was observed. Relative gene expression from qPCR analysis iv showed an up-regulation of gene expression of myosin light chain2 and myogenin by Arg, Gln and TTA treatments, while no effect of any treatment on gene expression of cathepsin L was found. However, TTA treatment showed a significantly lower expression of cathepsin B at 8°C. In addition, only the expression of cathepsin L was found significantly different between temperatures.