Biologging assessment of behavioural and physiological responses of European seabass (Dicentrarchus labrax) during stress challenges

Stress significantly impacts fish welfare, and for a comprehensive evaluation, welfare assessment requires an integrative approach. The objective of this study is to gain insight into the physiological and behavioural responses of European sea bass subjected to swimming and crowding stress tests through biologging. Individuals implanted with biologgers were subjected to swim tunnel and crowding tests, measuring locomotion, oxygen consumption, heart rate, acceleration and QRS-wave amplitude. During swimming stress tests, oxygen consumption correlated positively with heart rate (R² = 0.56, p < 0.001) and acceleration (R² = 0.76, p < 0.001). Acceleration values recorded by biologgers were strongly correlated with head and tail beat frequency (R² = 0.69 and R2 = 0.70 respectively; p < 0.001), validating heart rate and acceleration as reliable proxies for energy expenditure in sea bass. During the crowding challenge, heart rate increased progressively with each stressing event, while QRS-wave amplitude and acceleration peaked with stress but decreased in-between stressors. The assessment of physiological and behavioural responses of sea bass to swimming and crowding stress tests with biologgers allows the characterization of four welfare states, and therefore, highlights the potential of biologging for fish stress response and welfare monitoring.