Cardiac and behavioural responses to hypoxia and warming in free-swimming gilthead seabream, <i>Sparus aurata</i>

ABSTRACT Gilthead seabream were equipped with intraperitoneal biologging tags to investigate cardiac responses hypoxia and warming, comparing when fish either swimming freely in a tank conspecifics or confined individual respirometers. After tag implantation under anaesthesia, heart rate (fH) required 60 h recover stable value holding tank. Subsequently, undisturbed control conditions (normoxia, 21°C), mean fH was always significantly lower the than In progressive (100% 15% oxygen saturation), respirometers at levels down 40%, significant bradycardia both below this level. Simultaneous logging of tri-axial body acceleration revealed that spontaneous activity, inferred as variance external (VARm), low invariant hypoxia. Warming (21 31°C) caused tachycardia no differences between conditions. Mean VARm was, however, higher during positive relationship across all temperatures. Therefore, activity contributed raising warming. had highly linear rates uptake, considering data from warming together. The high indicates respirometry techniques may bias estimates metabolic traits some fishes, on free-swimming will provide more reliable insight into behavioural environmental stressors by their natural environment.