Crude and pre-extruded products of wheat as nutrient sources in extruded diets for Atlantic salmon ( Salmo salar, L) grown in sea water

Abstract

Atlantic salmon with initial mean weight 175 g, grown in sea water for 101 days, were fed extruded diets containing either 0, 15, 30 or 45% crude whole wheat (WC), pre-extruded whole wheat (WE) or pre-extruded after-meal (AE). After-meal is a protein-rich wheat by-product. In the WE diet series, we found growth (weight increase) to be significantly lower in the 45% diet than in the control diet, but although not statistically significant, there was a tendency towards reduced growth also in the other diet series, with increasing dietary inclusions of wheat. Condition factors were not affected by diet, and no significant differences were found in proximate carcass composition between fish fed the control diet or the diet contributing the highest amount of energy as carbohydrates. Plasma glucose, liver glycogen and hepatosomatic indices were within the normal ranges for all diets. No significant effects of wheat inclusion level were found on digestibilities of protein or lipid in any of the diet series. Starch digestibility was significantly higher in the diet containing 45% pre-extruded after-meal than in the diets containing 45% pre-extruded whole wheat or 45% crude whole wheat. The highest inclusions of wheat resulted in reduced dry matter digestibility in the pre-extruded whole wheat series and in the crude whole wheat series.