Struggling to breathe: small salmon struggle with hypoxia more than larger salmon

Dissolved oxygen is fundamental to the fitness and survival of fish. When there is not enough oxygen available in the water, hypoxic conditions occur which can have significant implications for the growth, feed intake and survival of fish. Monitoring dissolved oxygen saturation is one of the most important environmental factors analysed in Atlantic salmon aquaculture. To mimic the reduced oxygen levels experienced by fish in crowded streams and in commercial salmon aquaculture farms, researchers from the Institute of Marine Research, including SALTT-lab alumni Dr Tina Oldham, researched how fish of different sizes coped with hypoxic conditions. They tested how metabolic rate and swimming performance of Atlantic salmon in three size classes (0.2, 1.0 and 3.5 kg) were affected by exposure to 45-55% dissolved oxygen saturation. They found that while hypoxia did not affect standard metabolic rate, it caused a significant decrease in maximum metabolic rate and resulted in reduced aerobic scope. Further, swimming speed for small (0.2 kg) salmon was reduced by 23%, whereas large (3.5 kg) salmon were able to have slightly lower or similar swimming speeds compared to standard conditions. Their research illustrated that moderate hypoxia reduces the capacity for activity and movement in Atlantic salmon, with smaller salmon most vulnerable to hypoxic conditions.

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