Protein-nitrogen flux and protein growth efficiency of individual Atlantic salmon (Salmo salar L.)

Protein-nitrogen flux (the proportions of consumed and absorbed protein-nitrogen partitioned into protein synthesis and growth) was examined in Atlantic salmon, Salmo salar L. Salmon were held in groups and fed high or low rations or starved. Individual food consumption rates were measured using radiography. Fish varied widely in protein growth efficiency (protein growth divided by protein consumption), but this did not correlate with consumption rate, digestive capacity (as measured by absorption efficiency, trypsin levels and pyloric caecal size) or feeding hierarchy rank. Protein synthesis rates, measured in whole-animals, were linearly correlated with protein consumption and assimilation. There was a significant correlation between protein growth efficiency and the efficiency of retention of synthesised proteins. The capacity for protein synthesis and RNA activity were positively correlated with rates of food consumption and growth but were not correlated with protein growth efficiency. It was concluded that individual differences in protein growth efficiency related to differences in synthesis retention efficiency, but not to differences in the capacity for protein synthesis, RNA activity, digestive capacity or feeding hierarchy rank.