May 15, 2015: Opah

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You thought we had figured everything out. Well no. Here is the first known species of fully warm-blooded fish, the opah.

Fish that typically inhabit such cold depths tend to be slow and sluggish, conserving energy by ambushing prey instead of chasing it. But the opah’s constant flapping of its fins heats its body, speeding its metabolism, movement and reaction times, scientists report today in the journal Science.

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 of NOAA Fisheries’ Southwest Fisheries Science Center in La Jolla, Calif., lead author of the new paper.

“Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments,” Wegner said. “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.”

The opah has a weird radiator-like system of blood vessels. Vessels that get oxygen from the gills come back cold, because they have to get that oxygen from the surrounding water. The opah has developed warmer blood vessels that wrap around these colder ones, in a strategy to warm them up quickly.

It gives them a remarkable advantage! Now that we've learned how special the species is, what will we do with it?

The opah’s rich meat has become increasingly popular in seafood markets.