Protein is the most expensive single component in fish feed and the quality of the dietary protein is decisive for the productivity of fish farming. When fish meal is partly replaced by plant protein in feed for organic fish it is especially important, that the amino acid profile of the plant proteins is corresponding to that in the fish meal, as it is not allowed to add artificial amino acids to feed for organic fish.
In addition to the amino acid profile the digestibility of the nutrients is important for the productivity of the fish production. The digestibility of the diets were determined in cylindrical tanks with the bottom of each tank being conical with a ball-valve at the outlet. At this outlet a container for collecting faeces was mounted.
The collection method was compared with the stripping method. For this purpose yttriumoxide was added to the feed as a marker. The protein digestibilities were close for both methods, i.e. about 91-93 % with the lowest values using the stripping method
