title: Is winter worse for stressed fish? The consequences of exogenous cortisol manipulation on over-winter survival and condition of juvenile largemouth bass.
abstract: Over-winter mortality is an important selective force for warm-water fish (e.g., centrarchids) that live in temperate habitats. Inherent challenges faced by fish during winter may be compounded by additional stressors that activate the hypothalamic-pituitary-interrenal axis, either before or during winter, leading to negative sub-lethal impacts on fish health and condition, and possibly reducing chance of survival. We used experimental cortisol manipulation to test the hypothesis that juvenile largemouth bass (Micropterus salmoides) exposed to semi-chronic elevation in cortisol prior to winter would experience higher levels of over-winter mortality, physiological alterations and impaired immune status relative to control and sham-treated bass. Over-winter survival in experimental ponds was high, averaging 83%, and did not differ among treatment groups. Over the study period, bass exhibited an average increase in mass of 19.4%, as well as a slight increase in Fulton's condition factor, but neither measure differed among groups. Hepatosomatic index in cortisol-treated bass was 23% lower than in control fish, suggesting lower energy status, but white muscle lipid content was similar across all groups. Lastly, there was no difference in spleen somatic index or parasite load among treatment groups, indicating no long-term immune impairment related to our cortisol manipulation. The current study adds to a growing body of literature on glucocorticoid manipulations where field-based findings are not consistent with laboratory-based conceptual understanding of multiple stressors. This suggests that field conditions may provide fish with opportunities to mitigate negative effects of some stressors.
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada. Electronic address: tr.binder@gmail.com.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Binder
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada.
authors.forename: Constance M
authors.initials: CM
authors.lastname: O'Connor
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada.
authors.forename: Sarah H
authors.initials: SH
authors.lastname: McConnachie
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada.
authors.forename: Samantha M
authors.initials: SM
authors.lastname: Wilson
authors.affiliation: Sam Parr Biological Station, Illinois Natural History Survey, 6401 Meacham Rd., Kinmundy, IL 62854, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Nannini
authors.affiliation: Illinois Natural History Survey, University of Illinois, 1816 South Oak St., Champaign, IL 61820, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Wahl
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada; Institute of Environmental Science, Carleton University, 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Cooke
mesh_terms: D000818:Animals; D001492:Bass / Q000502:physiology*; D006854:Hydrocortisone / Q000008:administration & dosage*; D012621:Seasons; D013312:Stress, Physiological; D015996:Survival Rate
chemical_list: D006854:Hydrocortisone
keywords: Carryover effects; Glucocorticoid manipulation; Hepatosomatic index; Juvenile centrarchids; Micropterus salmoides