http://news.discovery.com/animals/first-warm-blooded-fish-identified-150514.htmhe opah, or moonfish, is the first known fully warm-blooded fish, according to a study published in the journal Science. The determination helps to explain why opah are such high performance predators that have a keen sense of vision, swim speedily, react quickly, and have the stamina to chase down fast-moving prey. “Before this discovery I was under the impression this was a slow moving fish, like most other fish in cold environments,” lead author Nicholas Wegner said 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 a fisheries biologist at NOAA Fisheries’ Southwest Fisheries Science Center in La Jolla. He first became aware that opah were unlike other fish when a colleague, Owyn Snodgrass, collected a sample of an opah’s gill tissue. Wegner noticed that the tissue had blood vessels to carry warm blood into the fish’s gills. The blood vessels then wound around those carrying cold blood back to the body core after absorbing oxygen from water. Engineers call this a “counter-current heat exchange.” In this case, the car radiator-like system means that warm blood leaving the fish’s body core helps to heat up cold blood returning from the respiratory surface of the gills where it absorbs oxygen.
