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Chronic exposure to high-temps has ‘few impacts’ on Atlantic salmon stress levels: study

The potential of using eye darkening as a non-invasive indication of stress was shown in a study that examined and developed temporal response profiles of physiological indicators of stress and growth in juvenile Atlantic salmon.

September 13, 2018  By Ruby Gonzalez

The study conducted in Australia by Tromp, Jared & L. Jones, Paul & S. Brown, Morgan & A. Donald, John & A. Biro, Peter & O.B. Afonso, Luis, and published in Aquaculture, exposed the fish to 12 °C, 16 °C, and 20 °C water temperature for 99 days.

“This study showed a clear physiological stress response (elevated levels of cortisol) and eye darkening in fish maintained at 16 °C but not at 12 °C or 20 °C, suggesting that some aspects of the physiological responses available to deal with chronic stress are affected by temperature. Eye darkening also did not differ between modes, but increased significantly in the groups exposed to 16 °C and 20 °C when compared with 12 °C,” the authors cited.

Cortisol is a steroid hormone that helps the body respond to stress.

Overall, the tests showed there are few impacts on stress physiology and growth responses in juvenile Atlantic salmon exposed long-term to increased water temperature.


There were no significant differences in fish body mass and length among the temperatures after 99 days. The findings were the same with plasma glucose and cholesterol levels.

While body mass at 12 °C and 20 °C were similar at the end of the study, fish maintained at the lower temperature were longer.

The authors noted that with previous studies about metabolic effects of high water temperatures in Atlantic salmon conducted for relatively short period of time, “information regarding the effects of chronic exposure to high water temperatures is poorly known in this species.”

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