Why are some fish warm-blooded? Predatory sharks gain speed advantage

Marine biologists have new research that reveals the answer to a fundamental question that has remained unsolved for decades: Why are some fish warm-blooded while others aren't? It turned out that although warm-blooded fish can regulate their body temperature faster, they cannot live in water with a wider range of temperatures. This research provides direct evidence of the evolutionary advantage of being warmer-blooded. It also underlines the fact that some species in this group - like the white shark and the bluefin tuna, are just as susceptible to changes in global ocean temperatures than their cold-blooded cousins. Lucy Harding (PhD Candidate at Trinity College Dublin's School of Natural Sciences) is the first author of the research article. It was published in Functional Ecology. She stated: Scientists know that not all fish can be cold-blooded. Although some fish have the ability to heat their bodies, it is not clear what benefits this ability has. Some believed that being warm-blooded enabled them to swim faster as their muscles are more powerful. Others believed that it allowed them live in warmer temperatures and was therefore more resistant to the impacts of ocean warming. Lucy and her international team of collaborators evaluated these possibilities by collecting data from bony fish and wild sharks, as well using existing databases. They were able to attach biologging devices to the fins and capture information about the fish they caught. This included water temperatures, speeds of swimming, depths of water, and how fast they were moving. These results revealed that although warm-blooded fishes were able to swim at least 1.6 times faster than those of cold-blooded relatives they also lived in much greater temperature ranges. Nick Payne is Assistant Professor in Zoology at Trinity's School of Natural Sciences. "The warm-blooded fishes have a faster swimming speed which gives them competitive advantages in areas like migration and predation. Predation aside, the hunting skills of bluefin tuna and white shark help to illustrate why this ability may be a competitive advantage. "Additionally, contrary to previous opinions and studies, our research shows that these animals don't live in warmer temperatures, which suggests that they could be equally at risk from the adverse effects of ocean warming. These findings, while they are interesting in their own right, can be very useful as they will aid in future conservation efforts for threatened animals. ### Science Foundation Ireland supported the research.

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