An increase of water temperature due to global warming is expected to be stressful for many aquatic species such as cold-water fishes. Otolith asymmetry is known to be a proxy of fish stress. However, Cottus gobio Linnaeus, 1758 inhabiting potentially stressing (i.e. warm) thermal conditions did not present a higher level of asymmetry in their otoliths than other ones. Local adaptations to thermal stress of the different populations studied or a weak a priori definition of the thermal tolerance of this species are discussed.