Farming of Atlantic halibut had its modest start in the 1980s and has slowly grown into an industry that sold 1900 metric tons in 2020. This has been a challenging endeavor where one bottle neck has replaced the next, and the first decades were largely dedicated to solving difficulties related to larval development. However, the industry has endured, and the current focus has moved from early development to optimalization growth and welfare to market size. We have therefore investigated the effect of varying levels of the macronutrients (protein, lipids and carbohydrates) on the grow out phase. Twelve diets were designed ranging in protein from 45 to 77 %, lipids ranging from 5 to 30 % and carbohydrates from 5 to 25 % of the diet. This represents a three-component mixture design, allowing analysis of the mixed effect of the factors on the fish. Atlantic halibut juveniles (mean weight, 300 g ; 120 in each tank) were randomly distributed to 15 tanks for one year .
The effect of macronutrients on growth changed during the growth period. In the start of the trial both high levels of carbohydrate and lipid had a negative effect on SGR, whereas the negative effect of high carbohydrate was less important toward the end of the trial. There was no effect of diet composition on digestibility of lipids and proteins. Muscle composition was not affected by diet composition, but the liver composition reflected dietary variations. Effects on appetite and welfare will be presented and discussed.