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Summary of Technical Literature Examining the Physiological Effects of Temperature on Salmonids

May 1, 2001


The chief objective of this paper is to provide a literature review of the role temperature exerts on the physiology of various salmonids. The fish are affected as species and within the stages of their life history. The thermal environment, perhaps more than any other aquatic habitat feature, influences the distribution, health and survival of our native salmonids. Temperature tolerances for salmonid species typically refer to effects of temperature on an individual. Because we are interested in sustainable populations of salmonids, this paper also reviews information on the optimal or preferred ranges of temperatures that will be needed to promote long-term survival, growth, and reproductive success. Thermal stress occurs when a temperature or a change in temperature produces a significant change to biological functions leading to decreased likelihood of survival. Thermal stress can lead to lethal effects either immediately, in a period of days, or even weeks or months from the onset of the elevated temperature. Thermal stress can also result in ‘sublethal’ or indirect effects resulting in death or reduced fitness that impairs processes such as growth, spawning, smoltification, or swimming speed. Metabolic processes are directly related to temperature, and the metabolic rate increases as a function of temperature. Fish are metabolically efficient and most likely to thrive within the preferred range of temperatures. Different species of salmonids have evolved to utilize different thermal regimes, although there is much overlap in their utilization of these regimes. Anadromous salmonids and coastal cutthroat and rainbow trout tend to have similar temperature requirements; however, where multiple species and life stages are present, temperature criteria need to protect the most sensitive species and life history stage. For this guild, maximum growth and swimming speed occur at 55.4-68°F (13-20°C) under satiation feeding; reduced ATPase levels are experienced at temperatures as low as 51.8-55.4°F (11-13°C), potentially resulting in delayed or ineffective smoltification; adult migration may be blocked at 69.8-73.4°F (21-23°C); and temperatures of 42.8-50°F (6-10°C) or lower during incubation result in maximum survival and size at emergence. Bull Trout have lower temperature requirements than other salmonids with optimal incubation occurring at 35.6-42.8°F (2-6°C), spawning being initiated as temperatures drop below 48.2°F (9°C), and the maximum growth rate at satiation feeding occurring at 60.8°F (16°C). For other salmonids such as Redband Trout, Westslope Cutthroat Trout, and Mountain Whitefish, little information is available on the effects of temperature on their physiology.


Dale McCullough, Shelley Spalding, Debra Sturdevant, and Mark Hicks


McCullough, D., S. Spalding, D. Sturdevant, and M. Hicks. 2001. Issue paper 5: summary of technical literature examining the physiological effects of temperature on salmonids: prepared as part of EPA Region 10 Temperature Water Quality Criteria Guidance Development Project. Seattle, WA, U.S. Environmental Protection Agency, Region 10. 118p.



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Inter-Agency Report