Climate Change Could Cause Heart Break in Atlantic Salmon

By: Abbey Floyd

Many of us have been outside in high temperatures and felt fatigued, out of breath and miserable. The same goes for animals. They also feel the repercussions of the increasing temperatures across the globe. With climate change becoming more and more of a concern, there have been many studies investigating how the physiology of organisms is being impacted. Carlie Muir and colleagues from the University of Western Ontario decided to dive into a gap of knowledge regarding how the hearts of young Atlantic salmon (Salmo salar) will respond to being exposed to higher temperatures than what they are used to. The aim of this study was to determine if Atlantic salmon can change the shape (and therefore the efficiency) of their hearts as a response to temperature stress.

The study focused on the juvenile salmon raised from eggs that were consistently exposed to water with an elevated temperature from the point at which the eggs were fertilized until 1-1.5 years later. After about a year, the research team used ultrasound technology to measure how powerful the heartbeat was (stroke distance) and how much blood is being pumped per heartbeat (cardiac output), as well as the maximum heart rate in response to the temperature increase. To determine how the structure or shape of the heart changed, the team took measurements of heart valves and the roundness and area of the ventricle, which is a muscular section of the heart that is responsible for pumping blood through the body. They also measured the thickness of the ventricle as a way to establish how hard the heart must work.

Muir and colleagues came across a potential obstacle relating to temperature and heart function. As temperature increases, the need for oxygen also increases which causes the body to increase heart rate but decrease power of the heart beats in order to deliver sufficient oxygen to the rest of the body. This finding makes it difficult to determine how exactly temperature will impact the cardiovascular system because the body acts to preserve heart function for as long as possible before detrimental effects take over.

However, the research team concluded that the Atlantic salmon were capable of adapting their heart function to the increased temperatures when they are exposed to those temperatures from fertilization. The fish were able to maintain a healthy heartbeat in higher temperatures than salmon raised at lower temperatures. In addition, salmon raised in warmer temperatures had significantly more dense heart muscle cells. This suggests that the oxygen supply to the heart becomes increasingly important as temperatures increase because if the cells of the heart do not have adequate oxygen, they will fail to function properly.

Although it has been shown that Atlantic salmon and other fish can alter the shape of their heart in response to increased temperatures, this is only effective to a point. Once the environmental conditions exceed the threshold in which the changes can accommodate for, the fish may begin to struggle. These changes to the heart can have lasting changes on the structure and the overall performance of the species going into the future. Specifically, the cardiovascular abilities/characteristics will be altered which could potentially lead to different challenges for the species during strenuous exercise (i.e., migrations) or during inadequate conditions (i.e., limited oxygen). Overall, these challenges could lead to declines in health and subsequently cause declines in populations. The study is significant in the fact that climate change and the subsequent increases in temperature will affect different species, populations and life stages of fish in different ways as there is a large degree of diversity in their ability to adjust. So next time you’re struggling in the heat, just know that you’re not the only one.

Muir, C. A., Garner, S. R., Damjanovski, S., Neff, B. D. (2022) Temperature-dependent plasticity mediates heart morphology and thermal performance of cardiac function in juvenile Atlantic salmon (Salmo salar). Journal of Experimental Biology. 225 (16), jeb244305.