The Opah, also known as the moonfish, is the world's fish to be identified as warm-blooded, scientists revealed this week.
USA Today reported that researchers from the National Oceanic and Atmospheric Administration (NOAA) discovered that the Opah generates heat by flapping its fins, then uses special blood vessels in its gills to retain the heat and distribute it throughout its entire body.
"The Opah appears to produce the majority of its heat by constantly flapping its pectoral fins, which are used in continuous swimming," said biologist Nick Wegner, the lead author of the report, which was
published Friday in the journal Science.
"There has never been anything like this seen in a fish's gills before," he added.
While many cold blooded reptiles, amphibians, and fish generate heat as they move around — including some tuna and sharks who warm their fins through such movement — the moonfish's special "counter-current heat exchangers" enable what scientists call "whole-body endothermy." That type of heat circulation looks more like that of warm blooded animals, like mammals and birds, than it does the vast majority of fish.
The Opah is a large fish, averaging 100 pounds and 3- to 6-feet across. Some fisherman operating in the Pacific Ocean catch the Opah for its rich meat, but for the most part they remain untouched, deep water fish.
"Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments," said Wegner. "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."
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