Apparent protein digestibility and mineral availabilities in various feed ingredients for salmonid feeds

Apparent digestibility of protein and availability of minerals (Ca, K, P, Mg, Na, Cu, Fe, Mn, Sr, Zn) in various feed ingredients were determined for coho salmon and rainbow trout using yttrium oxide (Y2O3) as the inert marker and passive feces collection tanks. The feed ingredients were herring meal, menhaden meal, anchovy meal, deboned whitefish meal, poultry by-product meal, feather meal, soybean meal, corn gluten meal, wheat gluten meal, wheat middling and wheat flour. Apparent digestibility (%) of protein and availability (%) of minerals were determined as a fractional net absorption of nutrients from diets. Apparent digestibility of protein and availability of K was high (> 80%) in all feed ingredients, whereas digestibility of dry matter and availability of Ca, Cu, Fe, Mg, Mn, Na, P, Sr and Zn were variable among ingredients. Apparent availability (%) of mineral elements was not significantly correlated to the amount of nutrient intake (mu g nutrient g(-1) BW day(-1)) in any test diet. Net nutrient absorption (mu g g(-1) BW day(-1)) was positively correlated (P < 0.05) to the nutrient intake except for Mn, Fe and Ca. Fecal nutrient losses (mu g g(-1) BW day(-1)) were positively correlated (P < 0.05) to nutrient intake except for protein, Na, K and Zn. (C) 1998 Elsevier Science B.V.