Effect of feeding rate on nutrient digestibility in Atlantic salmon, Salmo salar L

Abstract A digestibility trial was conducted to examine the effect of ration on dry matter, gross energy, crude protein and phosphorus digestibility in Atlantic salmon. Duplicate groups of fish were fed 0.25, 0.5, 0.75, 1.0, 1.25 and 1.9% BW day-1. The faeces were collected using Guelph-type collectors for five successive days. Dry matter, protein and phosphorus digestibilities were all significantly (P < 0.05) affected by ration. Dry matter digestibility was significantly lower in fish fed 0.25% BW day-1 in comparison with 0.5, 0.75 and 1% BW day-1. Protein digestibility was significantly lower for 0.25% BW day-1 ration in comparison with 1.25% BW day-1. Phosphorus digestibility was significantly lower for 0.25% BW day-1 ration in comparison with all other treatments except 1% BW day-1. There were no significant differences for energy digestibility between fish fed different rations. The main effect was reduced digestibility at the lowest ration with no obvious relationship between ration and digestibility above this. This was explained by a relatively higher loss of endogenous faecal nitrogen and phosphorus at sub-maintenance ration.