Using bulk oxygen uptake to assess the welfare of adult Atlantic salmon, Salmo salar, during commercial live-haul transport

Adult Atlantic salmon are routinely live-haul transported at high densities for long periods of time as one of the last intensive processes in a commercial aquaculture operation before fish processing. Therefore, ensuring the welfare of these fish during transport is critical to product quality. As an indirect assessment of fish welfare during transport, flow-through respirometry was used on board a commercial live-haul vessel to measure bulk oxygen uptake rate (M˙O2) for large masses of salmon being transported for over 10 h. Bulk M˙O2 was 2.98 ± 0.13 mg O2 min− 1 kg− 1 after 1 h of transport and decreased to 2.03 ± 0.14 mg O2 min− 1 kg− 1 after 10 h of transport. These rates of oxygen uptake were comparable to the routine oxygen uptake rates previously measured in tank-raised adult Atlantic salmon and in individual wild Pacific salmonids using swim-respirometers. Therefore, the values for bulk M˙O2 suggest that salmon recovered quickly from any stress of loading and stress was low throughout the 10 h of live-haul, perhaps indicating that salmon welfare was acceptable during the live-haul transport procedures that we followed. Using a mixed effects regression model, we found that bulk M˙O2 was positively affected by water temperature, and calculated the temperature coefficient (Q10) to be 1.9–2.0 between 7.8 and 15.0 °C. The model also showed that loading densities between 62 and 150 kg m− 3 did not significantly affect bulk M˙O2.