Temperature and pressure dependency of oxygen consumption during long-term sustained swimming of European eels

Many aspects of the typically 5000-10000 km spawning migration of the European eel (Anguilla anguilla) remain unknown. As part of this migration, eels undertake extensive diurnal vertical migrations to depths below 1000 m, being exposed to a wide range of temperatures and hydrostatic pressures. In this experimental study, we exposed eels to different combinations of temperature (12 – 20 °C) and pressure (1 – 8 bar) during long term sustained swimming (32 – 47 d). Both temperature and pressure affected oxygen consumption rate, showing a significant increase of metabolic rate with temperature, whereas pressure reduced oxygen consumption, albeit only at higher temperatures. Average oxygen consumption rates range between 15 mg kg−1 h−1 (12 °C, 1 bar) and 30.2 mg kg−1 h−1 (20 °C, 1 bar), highlighting the remarkably high swimming efficiency of this species and, more importantly, indicating that past estimates of the cost of transport are potentially overestimated since they are often based on experiments conducted at atmospheric pressure at higher temperatures.