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First warm-blooded fish identified by researchers
The opah can circulate heated blood throughout its body, making it the first fish known to be fully warm blooded. - photo by Natalie Crofts
LA JOLLA, Calif. Despite living deep in cold water, the opah can keep itself warm.

Researchers recently made the discovery while collecting samples of gill tissue from opah, a silvery fish that is also known as a moonfish, according to the National Oceanic and Atmospheric Administration Fisheries. The NOAA team reported the fish can circulate heated blood throughout its body, making it the first fish known to be fully warm-blooded.

Nature has a way of surprising us with clever strategies where you least expect them, fisheries biologist Nicholas Wegner said in a statement. Its hard to stay warm when youre surrounded by cold water, but the opah has figured it out.

The opah has been found in oceans around the world and swims by rapidly flapping its large, red pectoral fins like wings through the water, according to NOAA. Researchers said they discovered blood vessels in the fishs gills, indicative of a counter-current heat exchange that carries warm blood into the gills and then sends cold blood back into the body core to conserve heat.

Having a warm-blooded body gives the opah an advantage over its competition, according to the study. Researchers said the fish can swim faster, see sharper and react quicker.

Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments, Wegner said. But because it can warm its body, it turns out to be a very active predator that chases down agile prey like squid and can migrate long distances.

Opah spend most of their time swimming at depths of 150 to 1,300 feet under the oceans surface, according to researchers. They said the fishs muscle temperature was about 41 degrees fahrenheit above the waters temperature on average.

Other underwater creatures, like some tuna and sharks, are able to briefly warm parts of their bodies to improve performance, but quickly cool down, according to NOAA.

The opah study was published in the journal Science on Tuesday.
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