Thermal Plasticity and Performance Adaptations in Gadid Muscle: Consequences for Activity and Lifestyle

A recently developed model of thermal tolerance proposed that a hierarchy of biological functioning exists, each level of which displays different thermal tolerances. As the hierarchy is ascended from a molecular and biochemical level, through cellular, organ, systemic, whole animal and ultimately ecological levels, the windows of thermal tolerance narrow. The current study looked at the thermal plasticity and adaptational mechanisms at selected biological levels of cod populations from the North East Arctic (NEAC), the North Sea (NSC) and Newfoundland (NFC), to explore their potential impacts on activity and lifestyle.Mitochondrial proliferation and increased myoglobin expression, in combination with the reduced kick and glide duration and a lower swimming efficiency all point to a metabolic shift from anaerobic pathways at 10 degrees C, towards a greater dependence on aerobic metabolism at 4 degrees C. All Atlantic cod populations were able to maintain cellular and biochemical, physiological and systemic functioning between 4 degrees C and 10 degrees C. Although biochemical, physiological and whole animal performance were reduced at 4 degrees C, acclimation temperature had no effect. The thermal flexibility of the examined functions at the different levels of organisation observed in the current study between 4 degrees C and 10 degrees C is evidently a requirement of living in the thermally unstable environment in which Atlantic cod find themselves.