Rise in body temperature helps fish swim faster

Not so cold-blooded creatures! A rise in body temperature enables certain species of fish to maximise their swimming distance and speed, a new study has found.
Marine scientists have long known that some species of fish possess a unique physiological characteristic - a web of arteries and veins lying very close together - that enables them to raise their internal temperatures higher than that of the water surrounding them.
Now, a new study by an international team of scientists has demonstrated that species possessing the ability to warm their core - a process called endothermy - are able to swim two and a half times faster than those whose body temperature doesn't change.

These species, which include some sharks and tunas, can also swim twice as far - ranges comparable to those of warm-blooded animals such as penguins and other marine mammals.
"The cost of moving faster and farther is high so there has to be an ecological reason that outweighs the physiological expenditure," said research biologist Jenn Caselle University of California, Santa Barbara.
"These endothermic fishes are putting a lot more energy into each unit of movement than their cold-blooded counterparts are," Caselle said.

"In fact, the estimated cost of transport is twice as high, but in return they're getting benefits from that increased swimming speed and wider range of migration," she added.

"We hypothesise these gains allow these endotherms to be more efficient hunters and to span larger areas in their migration, which probably provides feeding and reproduction benefits," said Caselle.
The team combined existing data with new information they obtained by attaching sensors - designed and built by lead author Yuuki Watanabe of Japan's National Institute of Polar Research - to several sharks in different locations around the world.
The researchers' analysis suggests that warmer "red" muscle endothermy permits speedier cruising and greater endurance, which in turn enables these fishes to swim long distances relatively quickly.
This characteristic, the marine scientists speculate, allows the fishes to take advantage of seasonally variable food sources.

Of those examined in the study, four shark species are endothermic - salmon, porbeagle, white and shortfin mako - as are five species of tuna - yellow fin, southern bluefin, Atlantic bluefin, Pacific bluefin and albacore.
One species in particular, the white shark, has a migration range greater than that of the humpback whale.
Of specific interest, Caselle noted, is the fact that endothermy evolved independently in these distinctly different groups of fishes.
The findings appear in the journal PNAS.