Efficiency of feed utilization in Atlantic salmon (Salmo salar L.) fed diets with increasing substitution of fish meal with vegetable proteins

Atlantic salmon smolts were fed for 15-week diets where 28% and 55% of the fish meal, respectively, were replaced by a mixture of full-fat soybean meal and maize gluten meal in comparison with a diet where 89% of the protein came from fish meal and the remainder from full-fat soybean meal and maize gluten meal. The diets were equal in gross energy, crude protein, lipids, carbohydrates, lysine and methionine plus cystine. Apparent digestibilities of energy and protein in fish meal, full-fat soybean meal and maize gluten meal were determined as 93.5% (19.5 MJ digestible energy (DE) kg(-1)) and 89.3%, 69.3% (14.4 MJ DE kg(-1)) and 76.9%, and 78.6% (16.4 MJ DE kg(-1)) and 87.0%, respectively. Tested by ANOVA and orthogonal polynomials, a linear reduction that approached significance and with no significant deviation from linearity was found in growth, SGR and TGC with increasing substitution of fish meal. Substitution of fish meal caused a significant linear reduction in the condition factor, while feed consumption was not affected. The effect of substitution on feed conversion ratio (FCR = g feed g(-1) growth) showed a near significant deviation from linearity, FCR being significantly higher on Diet 3 than Diet I and slightly lower on Diet 2 than Diet 1. Apparent protein digestibility of the test diets decreased significantly linearly with increasing substitution, while no significant effects were found on digestibility of lipids and gross energy. Carbohydrate digestibility was low with no significant differences between diets. Fish meal substitution had no significant effect on carcass content of moisture, protein, ash or energy, while content of fat was nearly significantly linearly reduced. Substitution caused a nominal insignificant linear reduction in protein accretion but had no effect on digestible protein consumption per gram of protein accretion. Protein efficiency ratio (PER = weight gain/protein consumption) decreased significantly curvilinearly and net protein value (NPV = carcass protein gain/protein consumption) significantly linearly with increasing substitution. Energy utilization for growth decreased significantly linearly with increasing substitution. There was a nominal linear reduction, which approached significance in energy accretion with increasing substitution. Substitution impaired energy utilization for energy accretion (i.e. increased MJ DE consumed/MJ accredited). (C) 2003 Elsevier Science B.V. All rights reserved.