Researchers Find World's First Warm-Blooded Fish

The silvery fish, roughly the size of a large automobile tire, is known from oceans around the world and dwells hundreds of feet beneath the surface in chilly, dimly lit waters.

• Researchers have discovered a first fully warm-blooded fish that circulates heated blood throughout its body much like mammals and birds.
• The silvery fish, roughly the size of a large automobile tire, is known from oceans around the world and dwells hundreds of feet beneath the surface in chilly, dimly lit waters.
• The warm-blooded opah or moonfish swims by rapidly flapping its large, red pectoral fins like wings through the water, giving it a competitive advantage in the cold ocean depths, reported the team from National Oceanic and Atmospheric Administration's National Marine Fisheries (NOAA Fisheries).
• "That warm-blooded advantage turns the opah into a high-performance predator that swims faster, reacts more quickly and sees more sharply," said fisheries biologist Nicholas Wegner, lead author of the paper.
• "It turns out to be a very active predator that chases down agile prey like squid and can migrate long distances," he added.
• While looking at opah, Wegner recognised an unusual design: Blood vessels that carry warm blood into the fish's gills wind around those carrying cold blood back to the body core after absorbing oxygen from water.
• The design is known in engineering as "counter-current heat exchange."
• Resembling a car radiator, it's a natural adaptation that conserves heat.
• The unique location of the heat exchange within the gills allows nearly the fish's entire body to maintain an elevated temperature even in the chilly depths.
• "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," the authors said.
• Discoveries like this will help scientists understand the role species play in the marine ecosystem.