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Freshwater ecosystems are undergoing rapid thermal shifts, making it increasingly important to understand species-specific responses to these changes. Traditional techniques for determining a species’ thermal tolerance are often lethal and time consuming. Using the enzyme activity associated with the electron transport system (ETS; hereafter referred to as enzyme assay) may provide a non-lethal, rapid, and efficient alternative to traditional techniques for some species. We used largemouth bass Micropterus salmoides (Lacepede, 1802) to test the efficacy of using an enzyme assay to determine thermal tolerance and respiratory exploitation in response to variable acclimation temperatures. Three tissue types were dissected from fish acclimated to 20, 25, or 30 °C and used in ETS assays at temperatures ranging from 7.5 to 40 °C. While there were significant differences among tissue types and acclimation temperatures, maximal enzyme activity occurred from 25.23 to 31.91 °C. Fish lost equilibrium at 39–42 °C in traditional CTmax trials, significantly higher than the upper optimum range determined via enzyme assays. The ratio of enzyme activity to measured whole organism respiration rate decreased with increasing water temperature, with the largest changes occurring at the upper optimum thermal range determined by enzyme assays. Our results indicate that ETS analysis may prove useful for obtaining biologically relevant thermal tolerances.

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cover image Canadian Journal of Zoology
Canadian Journal of Zoology
Volume 102Number 2February 2024
Pages: 155 - 165


Received: 8 February 2023
Accepted: 14 August 2023
Accepted manuscript online: 23 August 2023
Version of record online: 16 October 2023


This article is part of a collection entitled "Respirometry as a tool to investigate physiological responses at a broad scale of biological organization and diversity".

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Key Words

  1. largemouth bass
  2. Micropterus salmoides (Lacepede
  3. 1802)
  4. critical thermal maxima
  5. thermal tolerance
  6. ETS



School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA
Author Contributions: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft, and Writing – review & editing.
U.S. Geological Survey, Alabama Cooperative Fish and Wildlife Research Unit, Auburn University, Auburn, AL 36849, USA
Author Contributions: Conceptualization, Formal analysis, Methodology, Writing – original draft, and Writing – review & editing.
Biology Department, Lincoln Memorial University, Harrogate, TN 37752, USA
Author Contributions: Conceptualization, Methodology, Resources, Investigation, and Writing – review & editing.
Russell A. Wright
School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA
Author Contributions: Conceptualization, Formal analysis, Funding acquisition, Methodology, Resources, Supervision, Writing – original draft, and Writing – review & editing.
School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA
Author Contributions: Conceptualization, Formal analysis, Funding acquisition, Methodology, Resources, Supervision, Writing – original draft, and Writing – review & editing.

Author Contributions

Conceptualization: EGS, SKB, LMH, RAW, DRD
Data curation: EGS
Formal analysis: EGS, SKB, RAW, DRD
Funding acquisition: RAW, DRD
Investigation: EGS, LMH
Methodology: EGS, SKB, LMH, RAW, DRD
Resources: LMH, RAW, DRD
Supervision: RAW, DRD
Writing – original draft: EGS, SKB, RAW, DRD
Writing – review & editing: EGS, SKB, LMH, RAW, DRD

Competing Interests

The authors declare there are no competing interests.

Funding Information

Auburn University SFAAS
Hatch program of the National Institute of Food and Agriculture, U.S. Department of Agriculture
This research was supported in part by Auburn University’s School of Fisheries, Aquaculture and Aquatic Sciences, The U.S. Army Corps of Engineers (ARMY-W912HZ-21-2-0029), and the Alabama Agricultural Experiment Station and the Hatch program of the National Institute of Food and Agriculture, U.S. Department of Agriculture.

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