The impact of varying feeding regimes on oxygen consumption and excretion of carbon dioxide and nitrogen in post‐smolt Atlantic salmon Salmo salar L.

Oxygen consumption, carbon dioxide excretion and nitrogen excretion from 2 kg Atlantic salmon Salmo salar L. were studied at land-based outdoor tanks, throughout a 10 day period. Fish were fed six feed rations (0 [fasting fish], 0.15, 0.30, 0.45, 0.60 and 0.75% BW day-1) of commercially extruded dry feed at two provision regimes: between 07.00-09.00 h and 19.00–21.00 h (periodic feeding); and between 07.00-21.00 h (continuous feeding). Fish were acclimatized to the feeding regime for 5 days prior to the start of the experiment. From days 5 to 10 of the study, oxygen consumption was measured automatically every 15 min. During day 10, carbon dioxide excretion, ammonia and urea excretion were measured hourly throughout a 24 h period. During the experiment, the water temperature and salinity were 8.5C and 33.5 ppt, respectively. Significant linear relationships between feed ration and metabolic rates were evident. Increased feed ration influenced oxygen consumption, carbon dioxide excretion, ammonia and urea excretion, ammonia quotient and the respiration quotient, proportionally. The two feed provision regimes caused the establishment of different daily rhythms in metabolic excretion. Only small differences in total daily excretion were however recorded for each feed ration. Ammonia and respiratory quotient results clearly showed that fish became more dependent on fat oxidation as an energy source, when feed was restricted.