Rainbow trout regulates lean body growth but does not adjust feed intake of diets non-limiting in protein with varying lipid levels

Feed intake(FI) of juvenile rainbow trout Oncorhynchus mykiss was assessed in relation to:1) the nutritional history and 2) the dietary macro-nutrient composition of diets being non-limiting in protein content.Three diets were formulated:the LL(low lipid) diet with 57%CP,11%fat and 16 kJ DE/g(on DM basis);the HL(high lipid) diet with 48%CP,26%fat and 22 kJ DE/g,which was obtained by substituting 15%of the complete ingredient mixture of LL by 15%fish oil;and the L10 diet with 57%CP,21%fat and 22 kJ DE/g.The L10 diet was formulated to have a similar CP level as diet LL and a similar digestible energy level as diet HL,by altering the starch to fat ratio in the LL ingredient mixture.Fish(90g,triplicates per treatment with each 100 fish) were fed to visual satiation during two consecutive 8-week phases and initial and final body composition was measured.During Phase 1,fish were fed either the LL or HP diet.At the start of Phase 2,both dietary groups of Phase 1 were split into three subgroups,which were fed diet HP,LL or L10 (triplicates per treatment with each 20 fish).