Nutrition of Atlantic salmon (Salmo salar);: the requirement and metabolic effect of lysine

The aim of the study was to determine the dietary lysine requirement of medium sized Atlantic salmon (376 +/- 46 g) given a high energy diet (23.6 KJ g(-1)) and to see if increased levels of lysine would effect the metabolism of arginine. Zein was used as a major protein source in the experimental diets, which were supplemented with synthetic amino acids to resemble the amino acid pattern of fish meal, with the exception of lysine. Dietary lysine contents ranged from 5.9 to 21.0 g kg(-1) dietary dry matter. The requirement of lysine was estimated at 16-18 g kg(-1) dry diet or 0.79-0.89g MJ(-1) digestible energy. The result was confirmed by a significant increase of free lysine in muscle if excess lysins was added to the diet. Fish fed the highest level of lysine did not increase growth and tended to show reduced levels of arginine and ornithine in plasma and muscle and reduced level of urea in plasma. These findings indicate a metabolic effect on the utilisation of arginine at high dietary levels of lysine. Lysine was also found to inhibit liver arginase of Atlantic salmon in vitro. (C) 1998 Elsevier Science Inc. All rights reserved.