Warm-Blooded Sharks Swim Two and a Half Times Faster Than Their Colder Cousins

When you think of fish, you may automatically think that they're cold-blooded. Yet some species of fish possess a unique physiological characteristic--a web of arteries and veins lying close together that enables them to raise their internal temperatures. Now scientists have found that these warmer fish can swim two and a half times faster than their cold-blooded cousins.

"The cost of moving faster and farther is high so there has to be an ecological reason that outweights the physiological expenditure," said Jenn Caselle, one of the researchers, in a news release. "These endothermic fishes are putting a lot more energy into each unit of movement than their cold-blooded counterparts are."

The researchers combined existing data with new information that they obtained by attaching sensors to several sharks in different locations around the world. The findings suggested that warmer "red" muscle endothermy permitted speedier cruising and greater endurance, which enabled these fish to swim long distances relatively quickly. This characteristic may allow the fish to take advantage of seasonally variable food sources.

Of the fish studied, four of the shark species were endothermic as were five species of tuna. One species in particular, the white shark, has a migration range greater than that of the humpback whale.

What's more interesting is that endothermy evolved independently in these different groups of fishes. The two taxonomic groups diverged more than 450 million years ago, and their common ancestor was most likely cold-blooded.

"This research begins to shed light on possible reasons why these endothermic fish evolved in this way," said Caselle. "Our paper contains almost every piece of electronically recorded information in the literature right now-and that's not a lot. We'd like to be able to expand the use of sensor-captured data to other groups of fishes in order to build a dataset we could analyze to see what different species are doing in terms of their movements and speed."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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