The swimming physiology of the European eel under regulable hyperbaric conditions
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Final Report Abstract
The SPEER project aimed at investigating different physiological aspects of female silver eels (Anguilla anguilla) during their spawning migration. Main project objectives were to analyze the influence of different environmental and physiological parameters on energy consumption of eels during swimming and to assess the effects of hyperbaric pressure and swimming on swimbladder physiology, gene expression and function with special emphasis on implications of Anguillicola crassus infestations. All experiments were conducted in a hyperbaric swim tunnel system that allows the assessment of O2-consumption of large fish under variable flow, temperature and pressure conditions. Effects of different temperatures and hydrostatic pressures on O2-consumption of eels were analyzed in a series of swimming experiments. To quantify the effects and interactions of pressure and temperature on the O2-consumption rate, eels were exposed to all possible combinations of three pre-defined temperatures (19°C, 15.5°C and 12°C) and two pressures (1 and 8 bar). No interaction between temperature and pressure was found, but the results revealed a significant positive effect within this temperature range on O2 consumption. In a second approach it was investigated if the energy demand of female eels is affected by progressing gonadal maturation. For this experiment eels constantly swam between one and 136 days (i.e. 43 to 5,875 km). Eels were weekly injected with salmon pituitary extract in order to initiate gonadal maturation, while a control group received injections of NaCl-solution. Preliminary data suggest a slight increase in oxygen consumption with progressing maturation, which could indicate an elevated energy demand for simultaneous locomotion and gametogenesis. The outcomes of this study provide valuable novel insights into the energy demand of female eels during endurance locomotion and maturation, the two processes driving the 5000 to 7000 km long spawning migration of the European eel. Together with the results from the first experiment, this information is crucial for a recalculation of the lipid reserves required for a successful completion of the eel’s complex life cycle. Under the lead of our project partners from the University Innsbruck, the effect of prolonged swimming under elevated hydrostatic pressure on swimbladder function was investigated. Transcriptomic analyses in gas gland cells revealed differences in gene expression between experimental and control eels. In addition, changes in transcription detected in eels with damaged swimbladders exceeded changes in eels with functional swimbladders by far, suggesting that the nematode infection reduces the stress resistance of eels. Remarkable was the number of transcripts related to cAMP dependent signaling pathways in eels with a functional swimbladder, supporting the assumption that cAMP signaling may be involved in the control of gas gland cell activity. So, despite an overall challenging experimental setup with a prototype hyperbaric swim tunnel respirometer system, SPEER significantly contributed to an improved understanding of the physiology of long-distance migration of the European eel, based on the collaborative effort of a multidisciplinary research team.
Publications
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(2020) Swimming under elevated hydrostatic pressure increases glycolytic activity in gas gland cells of the European eel. PLoS ONE 15(9): e0239627
Schneebauer G, Lindemann C, Drechsel V, Marohn L, Wysujack K, Santidrian E, Dirks R, Hanel R, Pelster B
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(2022). A novel hyperbaric swimming respirometer allows the simulation of varying swimming depths in fish respirometry studies. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 264
Wysujack K, Marohn L, Lindemann C, Illing B, Freese M, Pohlmann JD, Reiser S, Meskendahl L, Debes PV, Pelster B, Hanel R
