Nutrient absorption and growth of Atlantic salmon (Salmo salar L.) fed fish protein concentrate.

Absorption of amino acids was studied in Atlantic salmon fed moist diets where 0, 15 and 30% of the fish meal protein was replaced with concentrated fish silage protein prepared from whole minced herring or herring fillet offal (Clupea harengus). Blood samples were withdrawn at 0, 3, 6, 12, 24, 48 and 72 h post-feeding, and plasma-free amino acid concentrations were compared to those of fish deprived of food for 48 h. Fish fed fish protein concentrate showed similar or higher plasma amino acid concentrations than fish fed diets without any added fish protein concentrate. Maximum plasma amino acid concentrations occurred 3-12 h post-feeding, being fastest in fish fed the most soluble protein source. Effects of inclusion levels on growth and nutrient utilisation were studied in two experiments where either 0 to 30% or 0 to 40% of the fish meal protein was replaced with the fish protein concentrates tested. Fish fed diets where less than 15% of the fish meal protein was replaced by fish protein concentrate showed better growth compared to fish fed either none or higher inclusion levels. Protein accretion decreased in fish fed the high inclusion levels, and remained unaffected by lower inclusion levels. Protein synthesis measured as incorporation of labelled lysine was not significantly affected by the fish protein concentrate inclusion. It is assumed that the better growth obtained might be due to a lower protein breakdown. (C) 1999 Elsevier Science B.V. All rights reserved.