LA JOLLA, Calif., May 14 (UPI) -- The opah, or moonfish, occupies the dark, chilly depths of the world's oceans, using heated blood to keep warm and agile. It's the first fish found to be fully warm-blooded.
Researchers first became intrigued by the fish's circulatory system after biologist Owyn Snodgrass noticed a sample of a specimen's gill tissue featured a unique tangling of blood vessels. The blood vessels carrying warm blood into the fish's gills were wrapped around the vessels returning cold, oxygen-enriched blood to the body core.
It's a circulator system adaptation that resembles a car radiator, making warming up the fish's blood a more efficient process. Engineers call it a "counter-current heat exchange." The opah's high-energy swimming and fast metabolism combined with its gill-centric heat exchange allows the fish to maintain an elevated body temperature even in the cold waters of the deep ocean.
Research by NOAA scientists showed the moonfish's average tissue temperature was five degrees Celsius warmer than the surrounding water. The opah typically swims 50 to 1,000 feet below the ocean surface.
The opah's high-energy swimming warms its blood, and its warm blood propels the fish to new athletic heights. Its agility and speed dwarf its cold-water companions.
"Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments," Nicholas Wegner, a researcher with NOAA Fisheries' Southwest Fisheries Science Center in La Jolla, Calif., explained in a press release. "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 is the lead author of a new study on the opah's unique circulatory system, published this week in the journal Science. While other fishes have developed partial warm-bloodedness, the opah is the first to have fully developed the adaptation.
"Nature has a way of surprising us with clever strategies where you least expect them," Wegner said. "It's hard to stay warm when you're surrounded by cold water but the opah has figured it out."
In figuring out how to stay warm, the opah has enabled itself to swim faster, think and react more quickly and efficiently, make sharper turns and even see better