| dc.description.abstract | Atlantic salmon, Salmo salar L., is an anadromous carnivore living in fresh water during the first year(s) of life and migrating to the sea after smoltification. The early life period in fresh water and the first sea winter are the critical periods when genetic expressions, food utilization, and growth can be affected by the environmental conditions. Studies using modified and newly developed biochemical techniques have provided significant insights into growth mechanisms and genetics of growth in connection with food utilization under different environmental conditions. The evidence indicate that the utilization of dietary protein is the primary key biological process that influences nutrients influx (absorption and transport of amino acids), hormone insulin secretion, protein growth efficiency (ratio of protein to lipid – P/L ratio), health, maturation, and behaviour. The process is affected by internal factors (genetics, age, growth stage) and external factors (temperature, light, vaccine, quality and availability of food). Fish with higher growth capacity have higher protein growth efficiency, and higher dietary protein level affects an increase in skeletal growth (increase in length). Trypsin and chymotrypsin specific activities are important indicators for dietary protein levels and consumption rates. The protease activity ratio of trypsin to chymotrypsin (T/C ratio) is developed to indicate digestive efficiency and growth, independent of the specific activity levels of the two enzymes. Moreover, in vitro protein digestibility technique, for prediction of dietary quality on fish growth, is improved for comparisons of dietary quality effects within and between different fish species by standardizing the dialyzed crude enzyme extracts used for digestion of raw materials and diets with respect to trypsin activity. Maturing Atlantic salmon have higher food consumption rate than immature salmon at the early period of the spawning year. This is indicated by higher total protease specific activity (peptic and tryptic specific activities) around April, and females have greater response than males. The protease specific activities become lower later due to lower consumption from summer until maturity in winter. Fish with higher growth rate (higher pyloric caecal T/C ratio) have faster maturation rate, and will have a higher reduction in growth rate with lower pyloric caecal T/C ratio at maturation. Females with higher maturation rates have higher oocyte T/C ratio of trypsin-like to chymotrypsin-like activities in spite of lower trypsin-like and chymotrypsin-like specific activities in their oocytes. The T/C ratio is the unique key indicator in pyloric caeca for somatic growth as well as in oocytes for oocyte development (maturation rate), independent of the specific activity levels of the two proteases | |
