First Warm-Blooded Fish Found
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Researchers first suspected that something might be strange about the opah after analyzing a sample of the fish's gill tissue. According to the new study, published today (May 14) in the journal Science, the blood vessels in the tissue are set up so that the vessels carrying cool, oxygenated blood from the gills to the body are in contact with the vessels carrying warm, deoxygenated blood from the body to the gills. As a result, the outgoing blood warms up the incoming blood, a process called counter-current heat exchange.
"There has never been anything like this seen in a fish's gills before," Wegner said in a statement. "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 (humans) thought of it."
To confirm that these special gills helped the opah stay toasty, the researchers tagged a number of moonfish with temperature monitors and tracked the fish as they dove. The fish spend most of their time at least 150 feet (45 m) below the ocean surface. No matter how deep they dive, however, their body temperature stays about 9 degrees Fahrenheit (5 degrees Celsius) warmer than the surrounding water. Fat deposits around the gills and muscles help insulate the fish, the researchers found.
Built for speed
Warm blood gives deep-sea fish a boost, according to Wegner. The opah's muscles and nervous system likely function faster than an equivalent fish with cold blood. Other deep-diving fish, such as tuna and some sharks can shunt blood to certain body parts to keep them warm during deep dives. But these fish have to swim up out of the depths frequently to prevent their organs from shutting down.
http://www.livescience.com/50839-first-warm-blooded-fish-found.html
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