Chinook salmon immune systems impacted by acute heat
National Fisherman | October 15, 2025
By Margaret Bauman
Fall run Chinook salmon in California. Photo courtesy of A Birding Naturalist.
Fisheries researchers have concluded that Chinook salmon in shallow streams in western Canada will be impacted in the coming years by the frequency, duration, and intensity of heatwaves.
When salmonids encounter high water temperatures, it may increase their susceptibility to infectious disease, according to the research published by the University of Waterloo, in Ontario, Canada, and Yellow Island Aquaculture Ltd. on Quadra Island, British Columbia, in the online journal Elsevier.
Their research has found that the disproportionate changes in temperature for three consecutive days or longer have risen in recent years and are expected to continue increasing globally in the coming decades.
Heatwaves result in several downstream consequences, including increased water temperatures in shallow streams and rivers, and there is a strong positive correlation between daily water and air temperature. Shallow rivers are particularly susceptible to temperature fluctuations. For every 1 °C increase in air temperature, stream temperature correspondingly rises approximately 0.4–0.6°C.
Increasing water temperatures have several repercussions for teleost (ray-finned) fishes like salmonids, whose body temperatures fluctuate with their surrounding environment. Their physiological functions are influenced by water temperature.
Salmonids have an optimal growth temperature of between 11° and 17° C. They display behavioral and metabolic changes when exposed to acute changes in temperature. Researchers said that with the rise in global water temperatures, it is becoming increasingly likely that salmon will encounter water at their upper tolerance limit while they travel from saltwater to freshwater to spawn.
For salmon that spawn in summer and into the fall, increased water temperature is considered an important variable in spawning productivity, egg viability, and adult survival. When increased water temperatures last longer throughout the day, it leaves little time for acclimation to or recovery from high temperatures.
Thermal stress of salmon may result in temporary immunoincompetence, for example, by production and secretion of glucocorticoid hormones, such as cortisol, known to have immunosuppressive effects on salmon, or decreasing immune functioning altogether.
Given that, it is important to assess the effects of increased river temperatures to determine any sublethal impacts on salmonids, researchers said.
Wild salmon populations have been decreasing since the 1970s. Fisheries and Oceans Canada has reported that Chinook salmon populations are reaching critically low levels in Southern British Columbia. Along the American and Canadian coasts in 1990, there was a sharp decline in Chinook salmon catches, simultaneously with significant climate and aquatic environmental shifts.
Researchers now understand that climate change has the potential to severely affect the viability of Pacific salmon populations and that more research into the extent of this impact and how salmon respond to their environmental changes is crucial, the study said.
Rising water temperatures may also increase the potential of damage by infectious agents like Vibrio anguillarum, which causes vibriosis in over 50 species of fish, crustaceans, and bivalves. Researchers reported that mortality due to vibriosis has resulted in up to 100 percent of population losses and devastating economic losses in both wild and aquaculture populations of Chinook salmon.
