The swimming physiology of the European eel under regulable hyperbaric conditions

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In SPEER (The swimming physiology of the European eel under regulable hyperbaric conditions) we aim at investigating the effect of elevated hydrostatic pressure on the swimming physiology and energetics of migrating European silver eel at molecular (RNAsequencing, enzyme activities), tissue (swimbladder, gonads) and organismal (respiration) levels. Moreover, the interaction with factors such as parasitic infestation and pollutants (PCBs, heavy metals) will be examined in order to better define physiological requirements and thresholds for a successful spawning migration. We want to quantify and disentangle the individual risk potentials of the various factors affecting silver eels during their migration by:1) Performing short- to long-term swimming trials using three novel hyperbaric swimming tunnels to assess the swimming capacity and metabolic requirements of silver eels under pressure. So far, previous studies have investigated swimming in eels either at atmospheric pressure in swim tunnels, in pressurized chambers or, when combined, in very small water volumes and with short investigation periods. In SPEER, however, we will use swimming flumes with a large water volume (205 l) to simulate the initial spawning migration of large female eels under hydrostatic pressure for time periods up to a month. Additionally, we will create individual load schemes of PCBs, heavy metals and swimbladder parasites, to gain threshold values for projecting potential migration failure. 2) Assessing the effect of elevated (constant and variable) hydrostatic pressure on the functioning of the swimbladder at the molecular and biochemical level. It is currently unknown how the elevated hydrostatic pressure encountered during the spawning migration affects metabolic activity and performance of the swimbladder and its role as buoyancy organ. In this context we will also focus of the effect of toxicants (PCBs, heavy metals) and parasites (A.crassus) on metabolic activity of swimbladder tissue and the fundamental functioning of the swimbladder. 3) Investigating the effect of prolonged swimming under pressure on gonadal maturation. Female silver eels profit from hormone injections but often produce low quality eggs, which could be optimized by swimming exercise to create high quality gametes and eggs. By combining long-term swimming exercise with constant or variable hydrostatic pressure, we will create a more realistic environment that could help produce high quality gametes and accelerate the life-cycle closure of the European eel.