Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Damjanovski, Sashko

2nd Supervisor

Neff, Bryan D.

Joint Supervisor

Abstract

Anthropogenic climate change is expected to have pervasive impacts on the performance and viability of fishes, as increasing temperatures create aerobically constrained environments for many species. Given the rapid rates of projected temperature increases, it is critical to evaluate the capacity for fish to respond to a changing thermal environment through phenotypic plasticity. In this thesis, I examined the capacity for developmental plasticity in the thermal performance of juvenile Atlantic salmon (Salmo salar) reared under two thermal regimes from fertilization, and investigated potential mechanistic underpinnings within the cardiorespiratory system. Cardiac performance was examined using a noninvasive Doppler echocardiograph system originally designed for use in mice. This application represents a novel adaptation of this system and a significant contribution to the fish physiology toolbox. I found that a 4°C increase in developmental temperature significantly altered thermal performance at the level of the heart and enabled fish to maintain cardiac function to higher temperatures during acute warming. Developmental temperature did not mediate maximum cardiovascular capacity nor oxygen-carrying capacity of the blood. However, fish reared in elevated temperatures throughout development expressed morphological traits associated with cardiorespiratory robustness, including an increased proportion of vascularized compact myocardium and an increased respiratory surface area at the gills. Finally, I compared the ventricular proteomes of juvenile salmon reared in the two thermal regimes and found that rearing temperature altered the abundance of proteins associated with angiogenesis, oxidative metabolism, and protein homeostasis. Taken together, these patterns suggest an improved oxygen delivery system and enhanced oxidative capacity within the myocardium of fish exposed to warmer temperatures in early life. In all, I show that developmental temperature mediates acute thermal tolerance through plastic adjustments that preserve aerobic performance under high temperature conditions. This work enhances our understanding of the environmental contribution to thermal tolerance in fish and identifies cardiorespiratory strategies that may improve thermal resilience in juvenile salmonids. These findings have important implications for the conservation and management of this ecologically, economically, and culturally important species.

Summary for Lay Audience

Anthropogenic climate change is expected to have pervasive impacts on the performance and viability of fishes, as increasing temperatures create aerobically constrained environments for many species. Given the rapid rates of projected temperature increases, it is critical to evaluate the capacity for fish to respond to a changing thermal environment through phenotypic plasticity. In this thesis, I examined the capacity for developmental plasticity in the thermal performance of Atlantic salmon (Salmo salar) reared under current or projected future temperature conditions (+4°C) from fertilization, and investigated potential mechanistic underpinnings within the cardiorespiratory system. In a novel application, cardiac performance was examined in juvenile salmon using a noninvasive Doppler echocardiograph system originally designed for use in mice. I found that a 4°C increase in developmental temperature significantly raised the optimal temperature for cardiac performance and enabled fish to maintain cardiac function to higher temperatures during acute warming. Developmental temperature did not affect maximum cardiovascular capacity nor oxygen-carrying capacity of the blood. However, fish reared in elevated temperatures throughout development expressed morphological traits associated with cardiorespiratory robustness, including an increased proportion of vascularized compact myocardium and an increased respiratory surface area at the gills. Finally, I compared the ventricular proteomes of juvenile salmon raised in the two treatments and found that elevated rearing temperature altered the abundance of proteins associated with angiogenesis, oxidative metabolism, and protein homeostasis. Taken together, these patterns suggest an improved oxygen delivery system and enhanced oxidative capacity within the myocardium of fish exposed to warmer temperatures in early life. In all, I show that developmental temperature mediates upper thermal tolerance through plastic adjustments that preserve aerobic performance under high temperature conditions. This work enhances our understanding of the environmental contribution to heat tolerance in fish and identifies cardiorespiratory strategies that may improve thermal resilience in juvenile salmonids. This work also highlights an opportunity to improve salmon enhancement outcomes by strategically altering hatchery rearing environments. In all, these findings have important implications for the conservation and management of this ecologically, economically, and culturally important species.

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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