ABSTRACT
Many fish naturally encounter a daily cycle of hypoxia, but it is unclear whether this exposure hardens hypoxia-intolerant fish to future hypoxia or leads to accumulated stress and death. The rainbow trout (Oncorhynchus mykiss) is a putatively hypoxia-sensitive species found in rivers and estuaries that may routinely experience hypoxic events. Trout were exposed to one of four 135 h treatments in a swim-tunnel respirometer: (1) air-saturated control (20.7 kPa PO2); (2) diel cycling O2 (20.7–4.2 kPa PO2 over 24 h); (3) acute hypoxia (130 h at 20.7 kPa PO2 followed by 5 h at 4.2 kPa PO2); and (4) the mean oxygen tension (12.4 kPa PO2) experienced by the diel cycled fish. Some responses were similar in diel O2 cycled and mean PO2-treated fish, but overall, exposure to ecologically representative diel hypoxia cycles improved hypoxia tolerance. Diel hypoxia-induced protective responses included increased inducible HSP70 concentration and mean corpuscular hemoglobin concentration, as well as reduced plasma cortisol. Acclimation to diel hypoxia allowed metabolic rates to decline during hypoxia, reduced oxygen debt following subsequent exposures, and allowed fish to return to an anabolic phenotype. The data demonstrate that acute diel cycling hypoxia improves hypoxia tolerance in previously intolerant fish through the activation of cellular protective mechanisms and a reduction in metabolic O2 requirements.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: K.J.W., T.M.; Methodology: K.J.W., A.A.C., S.L., T.M.; Software: C.E.V.; Validation: K.J.W.; Formal analysis: K.J.W., C.E.V.; Investigation: K.J.W., A.A.C.; Resources: K.J.W., A.A.C., S.L., T.M.; Data curation: K.J.W.; Writing - original draft: K.J.W.; Writing - review & editing: K.J.W., A.A.C., C.E.V., S.L., T.M.; Visualization: K.J.W., T.M.; Supervision: S.L., T.M.; Project administration: S.L., T.M.; Funding acquisition: S.L., T.M.
Funding
This study was funded by Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grants to T.J.M. and S.G.L., and an NSERC undergraduate student research grant to K.J.W.
- Received April 27, 2019.
- Accepted June 28, 2019.
- © 2019. Published by The Company of Biologists Ltd
Article navigation
Related articles
Cited by...
More in this TOC section
Similar articles
Other journals from The Company of Biologists
JEB and COVID-19
We are aware that the COVID-19 pandemic is having an unprecedented impact on researchers worldwide. The Editors of all The Company of Biologists’ journals have been considering ways in which we can alleviate concerns that members of our community may have around publishing activities during this time. Read about the actions we are taking at this time.
Please don’t hesitate to contact the Editorial Office if you have any questions or concerns.
Announcing JEB's 2019 Outstanding Paper Prize
Congratulations to all of the authors whose papers were shortlisted for the 2019 JEB Outstanding Paper Prize. This year we had a great selection of papers and the final winners were Kephra Beckett and Anne Roberts, from the University of British Columbia, Canada, for their work on spittlebug breathing in xylem sap foam.
The Biology Open transfer option
JEB authors have the option to transfer their submission to our sister journal Biology Open. An online Open Access journal, BiO also welcomes direct submissions and focuses on the swift publication of high-quality, sound research. Recent comparative physiology highlights in BiO include the current cover article from Okuyama et al., who show that Green sea turtles have an immediate cardiac response to exercise during submergence. Find out more about how to transfer.
Mantis shrimp pull punches in air for self-preservation
In their new Short Communication, Feller et al. demonstrate that punches by mantis shrimp in air are slower and only one tenth of the power than in thick water.
What determines systemic blood flow in vertebrates?
To understand how systemic blood flow is regulated, Tobias Wang and William Joyce look at factors beyond the heart in their new Review.
JEB appoints new Editor-in-Chief
We are delighted to announce that Craig Franklin (University of Queensland, Australia) has been appointed as the next EiC of JEB, starting on 1 August. With research interests in animal ecophysiology and conservation physiology, Craig is already familiar with the journal, having been a Monitoring Editor since 2011. We are looking forward to welcoming him in his new role.