Scientists made the incredible discovery that the moonfish is warm-blooded.
The finding reveals the first warm-blooded fish known to science, NOAA Fisheries West Coast Region reported. The research suggest the warm blood coursing through the fish's body could give it a competitive advantage in the icy depths of the ocean.
Fish that live in cold, deep water are usually slow in nature, but this fish's warm blood allows it to move at high speeds in its frigid environment.
"Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments," said fisheries biologist Nicholas Wegner of NOAA Fisheries' Southwest Fisheries Science Center. "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."
Researchers noticed signs of vessels that carry warm blood when studying gill tissue from the moonfish, also known as an opah. They could tell the veins circulated warm blood because they wound back to the body core after absorbing oxygen from the water in the gills. This design is known as "counter-current heat exchange" in the engineering world, and is similar a car radiator.
"There has never been anything like this seen in a fish's gills before," Wegner said. "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."
To back up their findings, the researchers tested the body temperatures of opah caught during West Coast surveys, and found their body temperatures were regularly warmer than the surrounding water. Thermometers attached to the fish showed their body temperature remained steady even when they made deep dives. Some fish have limited warm-blooded qualities, but the researchers believe the opah developed its full warm-blooded system independently in cold water.
Scientists have observed a jump in California opah populations in recent years, but researchers are not sure what is causing this.
"Discoveries like this help us understand the role species play in the marine ecosystem, and why we find them where we do," said Francisco Werner, director of the Southwest Fisheries Science Center. "It really demonstrates how much we learn from basic research out on the water, thanks to curious scientists asking good questions about why this fish appeared to be different."
The findings were published in a recent edition of the journal Science.
