For over 50 years now, scientists have known that, despite their reputation, not all fish are cold-blooded. Some shark and tuna species, the white shark and the Atlantic blue fin tuna, have evolved the ability to warm parts of their bodies, such as their muscle, eyes and brain.
About 35 species of fishes – accounting for less than 0.1% of all described fishes – have this ability, which allows them to stay warmer than the surrounding water. Until recently, however, the reason this ability evolved was a mystery.
Some scientists believed being warm-blooded allowed the fish to swim faster, as warmer muscles tend to be more powerful. Others thought it allowed them to live in a broader range of temperatures, making them less susceptible to the effects of ocean warming caused by climate change. With this in mind, an international team of marine biologists and I set out to answer the puzzle of why some fish warm-blooded when most aren’t.
Our study found fishes’ ability to warm their bodies provides competitive advantages – they can swim faster than their cold-blooded relatives. However, this doesn’t necessarily mean they’ll be able to adapt to changing ocean temperatures under climate change better than cold-blooded fish, according to our results.
The silvery fish, roughly the size of a large automobile tire, is known from oceans around the world and dwells hundreds of feet beneath the surface in chilly, dimly lit waters.
Researchers have discovered a first fully warm-blooded fish that circulates heated blood throughout its body, much like mammals and birds.
The silvery fish, roughly the size of a large automobile tire, is known from oceans around the world and dwells hundreds of feet beneath the surface in chilly, dimly lit waters.
The warm-blooded or moon-fish swims by rapidly flapping its large, red pectoral fins like wings through the water, giving it a competitive advantage in the cold ocean depths, reported the team from National Oceanic and Atmospheric Administration's National Marine Fisheries (NOAA Fisheries).
"That warm-blooded advantage turns the fish into a high-performance predator that swims faster, reacts more quickly and sees more sharply," said fisheries biologist Nicholas Wegner, lead author of the paper.
"It turns out to be a very active predator that chases down agile prey like squid and can migrate long distances," he added.
While looking at fish, Wegner recognized an unusual design: Blood vessels that carry warm blood into the fish's gills wind around those carrying cold blood back to the body core after absorbing oxygen from water.
Resembling a car radiator, it's a natural adaptation that conserves heat.
The unique location of the heat exchange within the gills allows nearly the fish's entire body to maintain an elevated temperature even in the chilly depths.
This is a cool innovation by these animals that gives them a competitive edge.
"The concept of counter-current heat exchange was invented in fish long before we thought of it," the authors said.
Discoveries like this will help scientists understand the role species play in the marine ecosystem.
The paper appeared in the journal Science.
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