Aerobic exercise increases the utilization efficiency of energy and protein for growth in Atlantic salmon post-smolts

Aerobic exercise training may improve growth and help to protect fish from viral and bacterial diseases. This study was conducted to determine the effect of increased sustained aerobic exercise on the maintenance requirements and the efficiency of utilization of digestible protein (DP), digestible amino acids and metabolizable energy (ME) for growth above maintenance of Atlantic salmon post-smolts. The fish were held in tanks with currents of 7 (low speed) or 23 (high speed) cm s− 1 (initial speeds 0.32 and 1.06 body lengths s− 1) for 62 days and fed a fishmeal-based diet in excess or at levels approximating 30, 40, 60 and 80% of the intake of the full-fed groups. In the full-fed groups, there was no significant effect of exercise treatment on feed intake, final weights, growth rates, feed efficiency or whole-body composition. An extrapolation to zero weight gain showed that the increased speed resulted in an increase in the maintenance requirement from 5.3 to 13.4 g dry matter fish− 1. The maintenance requirement for ME, which includes the energy used for activity, was 46.5 kJ kg− 0.8 d− 1 in the high exercise groups and 24.7 kJ kg− 0.8 d− 1 in the low exercise groups. Our calculations showed that true maintenance, in which energy used for activity has been removed, was 15.3 kJ kg− 0.8 d− 1 at zero speed. Above maintenance, the efficiency of utilization of ME for energy gain was 0.89 in the high exercise groups and 0.70 in the low exercise groups (P < 0.05). The maintenance requirements for DP were three times higher in the high exercise groups than in the low speed groups, but above maintenance, DP was used more efficiently for protein gain in the high exercise groups (0.70) than in the slow groups (0.60) (P < 0.05). The efficiency of utilization of digestible arginine, histidine, isoleucine, leucine, lysine and phenylalanine for gain of these amino acids above maintenance tended to be greater in the salmon exercised at the high speed compared with those exercised at the low speed (P ≤ 0.1). The maintenance requirements for most of the digestible amino acids were about twice as high in the high speed groups compared with the low speed groups. These results show that with increased aerobic exercise, the higher activity costs of Atlantic salmon are associated with increased utilization of nutrients and energy for growth.