Availability of protein, phosphorus and other elements in fish meal, soy-protein concentrate and phytase-treated soy-protein-concentrate-based diets to Atlantic salmon, Salmo salar

An experiment with 0.1-kg Atlantic salmon in saltwater was conducted to evaluate soy-protein concentrate as a source of dietary protein and to determine if phytase treatment of soy concentrate affected the availability of protein and essential elements. Three diets were fed to triplicate groups of fish for 84 days: Diet 1 with 61% fish meal, Diet 2 with 50% soy concentrate and 16% fish meal, and Diet 3 with 50% phytase-treated soy concentrate, The soy concentrate contained 18 g phytic acid kg(-1), and no phytate remained after phytase treatment. Soy concentrate was equivalent to fish meal as a source of dietary protein for Atlantic salmon, and incubation with phytase resulted in improved protein digestibility, feed conversion, protein retention, and reduced metabolic N-excretion. Whole-body Ca, Mg, and Zn levels, apparent digestibility coefficients of the same elements, and retentions of P and Zn were lower in fish fed the untreated soy concentrate compared to the phytase treated soy. Whole-body concentrations of Ca, Sr and Zn were correlated to P independent of dietary treatment, but the ratios between P and the other elements were not constant. The faecal output of Na was high for both soy concentrate diets independent of phytase treatment. (C) 1998 Elsevier Science B.V.