Summary:
Three feeding trials were conducted to estimate the minimum protein requirements for maximum growth of Atlantic cod (initial size 37–600 g). The diets in each trial were near iso-energetic and contained 47–64% crude protein (CP) in dry matter for small fish while diets for larger fish contained 36–57% CP. There was no significant difference in the final weight of small fish (90–130 g) fed different levels of CP. However, the specific growth rate (SGR) of fish fed 59% and 64% CP (0.9% day−1) was significantly higher than that of fish fed either 47% or 48% CP (0.5–0.7% day−1). The hepato-somatic index (HSI) increased progressively with decreased CP and the feed conversion ratio (FCR) was negatively correlated with CP of the diets. In two trials with larger fish, CP did not significantly affect mean final weight (750–900 g), SGR or FCR. As for the smaller fish, the HSI was negatively correlated with CP and in one of the experiments, the feed intake was also negatively correlated with CP. The feed efficiency tended to be reduced. The results suggest that the protein requirement for maximum growth in Atlantic cod is size dependent: for 40–107 g fish, the minimum CP is 47–52% and for larger fish (400–900 g) it is 36% or lower.