The swimming physiology of the European eel under regulable hyperbaric conditions (SPEER)
Recruitment of the European eel has been in decline since the 1980s. So far, the population has not recovered and is considered „critically endangered“. The species has a complex life-cycle which still poses a variety of unresolved questions, including the effects of hydrostatic pressure on the eel’s metabolism. Detailed experimental studies could improve our knowledge on possible physiological changes during the long-distance spawning migration to the Sargasso Sea. With our novel hyperbaric swim tunnel respirometer system, the conditions during the early marine phase of the spawning migration can be simulated and the energy expenditure of the eels during swimming can be measured under controlled conditions.
During their approximately 6,000 km long migration to the Sargasso Sea, eels exhibit regular diel vertical movements (DVM) with amplitudes of several hundred meters, which already start in the near-coast shelf areas. As a consequence of these DVM, the eels are confronted with considerable changes in hydrostatic pressure. With changes of 0.1 MPa per 10 meter depth the variability of the pressure is comparable to other physical and chemical parameters, like temperature, salinity, oxygen concentration or light.
However, the effects of hydrostatic pressure on marine animals are complex and can in vivo be hardly separated from the effects of other factors.
Therefore, in an earlier project („Anpassung und Weiterentwicklung von innovativen, nicht-invasiven Monitoringsystemen und Auswerteverfahren für die Fischereiforschung“ AutoMAt; WP4 „Wie wandern Blankaale zurück ins Meer“), together with our partner Kunststoff-Spranger GmbH, our institute developed three hyperbaric swim tunnels with respirometer function. These will enable studying the effects of hydrostatic pressure at defined swimming speeds and temperatures on the energy balance of eels over longer periods.
In cooperation with the University of Innsbruck we will investigate the effects of hydrostatic pressure on the metabolism of eels during their spawning migration, thereby improving our understanding of potential effects of environmental factors like parasites or contaminants on the swimming capacity of eels. In addition, we will study if maturation processes of the eel gonads are influenced by pressure.
In the frame of the SPEER project we will conduct comprehensive experiments on the swimming physiology of European eels under controllable hydrostatic pressure. The accompanying investigations will be conducted on different levels: molecular (RNAsequencing, enzyme activity), tissue specific (swim bladder, gonads) and whole organism (respiration). We intent to conduct experiments of different length (short-, intermediate-, long-term).
The eels will be confronted with different currents, temperatures and pressures, which will reflect natural conditions.
As an important aspect, the experiments will be conducted with eels from different German river systems. Accordingly, the fish will differ in their condition at the start of the migration, in particular regarding infestation with parasites and contaminant load. These studies will shed light on the question, if and to what extent detrimental environmental factors affect the spawning migration and possibly prevent a successful reproduction.