title: Warm acclimation and oxygen depletion induce species-specific responses in salmonids.
abstract: Anthropogenic activities are greatly altering the habitats of animals, whereby fish are already encountering several stressors simultaneously. The purpose of the current study was to investigate the capacity of fish to respond to two different environmental stressors (high temperature and overnight hypoxia) separately and together. We found that acclimation to increased temperature (from 7.7±0.02°C to 14.9±0.05°C) and overnight hypoxia (daily changes from normoxia to 63-67% oxygen saturation), simulating climate change and eutrophication, had both antagonistic and synergistic effects on the capacity of fish to tolerate these stressors. The thermal tolerance of Arctic char (Salvelinus alpinus) and landlocked salmon (Salmo salar m. sebago) increased with warm acclimation by 1.3 and 2.2°C, respectively, but decreased when warm temperature was combined with overnight hypoxia (by 0.2 and 0.4°C, respectively). In contrast, the combination of the stressors more than doubled hypoxia tolerance in salmon and also increased hypoxia tolerance in char by 22%. Salmon had 1.2°C higher thermal tolerance than char, but char tolerated much lower oxygen levels than salmon at a given temperature. The changes in hypoxia tolerance were connected to the responses of the oxygen supply and delivery system. The relative ventricle mass was higher in cold- than in warm-acclimated salmon but the thickness of the compact layer of the ventricle increased with the combination of warm and hypoxia acclimation in both species. Char had also significantly larger hearts and thicker compact layers than salmon. The results illustrate that while fish can have protective responses when encountering a single environmental stressor, the combination of stressors can have unexpected species-specific effects that will influence their survival capacity.
authors.affiliation: Laboratory of Animal Physiology, Department of Biology, University of Turku, Turku 20014, Finland katja.anttila@utu.fi.
authors.forename: Katja
authors.initials: K
authors.lastname: Anttila
authors.affiliation: Laboratory of Animal Physiology, Department of Biology, University of Turku, Turku 20014, Finland.
authors.forename: Mario
authors.initials: M
authors.lastname: Lewis
authors.affiliation: Laboratory of Animal Physiology, Department of Biology, University of Turku, Turku 20014, Finland.
authors.forename: Jenni M
authors.initials: JM
authors.lastname: Prokkola
authors.affiliation: Laboratory of Animal Physiology, Department of Biology, University of Turku, Turku 20014, Finland.
authors.forename: Mirella
authors.initials: M
authors.lastname: Kanerva
authors.affiliation: Natural Resources Institute Finland (Luke), Laasalantie 9, Enonkoski 58175, Finland.
authors.forename: Eila
authors.initials: E
authors.lastname: Seppänen
authors.affiliation: Natural Resources Institute Finland (Luke), Laasalantie 9, Enonkoski 58175, Finland.
authors.forename: Irma
authors.initials: I
authors.lastname: Kolari
authors.affiliation: Laboratory of Animal Physiology, Department of Biology, University of Turku, Turku 20014, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Nikinmaa
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D057231:Climate Change; D006352:Heart Ventricles / Q000033:anatomy & histology; D006358:Hot Temperature; D010100:Oxygen / Q000502:physiology*; D020317:Salmo salar / Q000033:anatomy & histology / Q000502:physiology*; D013045:Species Specificity; D014337:Trout / Q000033:anatomy & histology / Q000502:physiology*; D014876:Water Pollution
chemical_list: D010100:Oxygen
keywords: Cardiac system; Eutrophication; Gill; Hypoxia tolerance; Oxygen supply and delivery system; Temperature tolerance