An Opah fish was discovered by scientists from the National Oceanic and Atmospheric Administration to be the Pacific Ocean's first fully warm-blooded fish. The Opah fish, also called the moonfish, maintains the temperature throughout its body by circulating warm blood, just like humans and other mammals.
About the size of a car tire, the Opah fish roams an area of the ocean where most of inhabitants are slow and sluggish. Its rotund, silver body may be characteristics enough to marvel at, but the new discovery by researchers of it being warm blooded is certainly a surprise, even for scientists, reported Live Science.
"There has never been anything like this seen in a fish's gills before," said NOAA's Nick Wegner, biologist and lead author of the report on the Opah fish.
The Opah fish is unlike any other in that it generates heat by swimming and distributing warmth throughout their entire bodies with the use of special blood vessels. By constantly flapping its fins, the Opah is able to heat its body up and fuel its metabolism.
They also have special "counter-current heat exchangers" in their gills which minimize heat loss. This allows for deepwater predators, such as the Opah, to keep their bodies several degrees above the water temperature when they are 250 feet down the ocean, according to USA Today.
This feature gives them a kind of distinct predatory advantage because the Opah is able move more quickly than other sea predators.
"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."
Wegner, together with his team, were able to unravel the mystery of the Opah by attaching temperature monitors to the species off of the western United States, according to Discovery.
They found that the fish's temperature remained considerably warmer than its surrounding water temperature despite the change in the depths of the ocean.
Opahs reportedly don't swim in schools. They are usually caught by longline fishermen from California to Hawaii to New Zealand seeking tuna. They are also caugt unintentionally in commercial driftnets.
An old Opah fish tale, according to the NOAA, says that the fish brings good luck. Before, fishermen gave them away if caught rather than sell the Opah. However, times have changed, and many people are becoming food fetishists, demanding more of the fish's "rich, tasty meat."
For more information on the Opah fish by the NOAA, click here.
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