Nutrition of Arctic charr (Salvelinus alpinus) and Eurasian perch (Perca fluviatilis) and evaluation of alternative protein sources

The aim of this thesis was to estimate the dietary lysine requirement of Eurasian perch (Perca fluviatilis), to study the digestive enzyme activity in perch and Arctic charr (Salvelinus alpinus) and the utilization of meals of microbial and mussel meals. Juvenile Eurasian perch were fed semi-purified diets containing graded levels of lysine (12.2-24.3 g kg-1 dry matter (DM), (3.0-6.0 g/16 g nitrogen (N)) to estimate the lysine requirements. Fish fed diets containing 18.3-24.3 g lysine kg-1 DM had higher final body weight, weight gain, protein gain and specific growth rate than fish fed diet containing 12.2-17.3 g lysine kg-1 DM. The results indicate that the lowest lysine level required for optimal growth performance in Eurasian perch is 18.3 g lysine kg-1 DM (4.5 g/16 g N). The activity of digestive enzymes was studied in farmed Eurasian perch and Arctic charr. There were no differences in the activity of lipase, α-amylase and disaccharidases between slow and fast growing perch, or between perch of different age. The total lipase activity was higher than total carbohydrase activity in both species. Perch had a higher total activity of carbohydrases than charr, suggesting a greater capacity for digesting carbohydrates, especially starch. In Artic charr, the apparent digestibility coefficients (ADC) of dry matter (DM), amino acids (AA) and energy was lower for intact Saccharomyces cerevisiae than for extracted S. cerevisiae, Rhyzopus oryzae and Mytilus edulis, whereas the ADC of crude protein (CP) did not differ between the ingredients. With the exception for arginine and histidine, differences were found in ADC of indispensable amino acids (IAA) between the test ingredients. In Eurasian perch, there were no significant differences in the ADC of DM, CP, IAA and energy between the test ingredients. The results indicate that 40% of CP derived from fish meal in diets for Arctic charr can be substituted with blue mussel (M. edulis) meal or intact S. cerevisiae yeast without any negative effect on growth performance and nutrient utilization