Growth, uptake and retention of nitrogen and phosphorus, and absorption ofother minerals in Atlantic salmon Salmo salar fed diets with fish meal andsoy-protein concentrate as the main sources of protein

An experiment with 0.2-kg Atlantic salmon, Salmo salar in saltwater was con ducted to determine if the fish could grow normally, and maintain normal ni trogen (N) and mineral balance when fed a diet with the majority of the pro tein (75%) derived from soy-protein concentrate (SPC). The two diets contai ned 50% SPC and 15% fish meal (FM) or 60% FM as the sources of protein. No calcium phosphate was added to the diets in order to assess the availabilit y of P from the ingredients. A second aim was to investigate if whole-body concentrations of essential elements and growth were related in individual salmon. Growth (SGR=0.88-0.89) was similar in salmon fed the two diets, and the fis h nearly doubled their body weights during the 84 days of feeding. Feed con version was more efficient for the FM diet (0.81 kg intake kg(-1) gain) tha n for the SPC diet (0.89 kg kg(-1)). The intake of N was similar, faecal lo ss of N was lower, while the metabolic N excretion was greater in the fish fed the FM than the SPC diet. This resulted in a total excretion of 35.4 g N kg(-1) gain for the salmon fed the FM diet and 35.5 g N for the fish fed the SPC diet. Both the intake, faecal and metabolic excretion of P were hig her in the fish fed the FM diet than the SPC diet, resulting in a total exc retion of 10.5 g P kg(-1) gain for the FM diet and 7.2 g P for the SPC diet . Whole-body concentrations of Ca, Mg, P and Zn were lower in the fish fed the SPC diet, while the Ca-P ratio was decreased, both when compared with t he fish at the start of the experiment, and the fish fed the FM diet. The d ifferences in elemental composition were ascribed to a combination of reduc ed availability of elements due to phytic acid and lower concentration of e lements in the SPC than in the FM. No reduction in growth of individual fis h, which could be ascribed to reduced availability of essential elements, w as seen.