The car-tire-size opah is the first fish species found to be fully warm-blooded, circulating heated blood throughout its body much like mammals and birds, research has revealed.
“…the opah, a large deepwater fish, can generate heat with its swim muscles and use this heat to warm both its heart and brain. This ability increases its metabolic function in cold deep waters, which will help the fish compete with other, colder-blooded species,” reads the publication.
Generally, fish inhabiting cold depths are slow. They need to conserve their energy to ambush prey. But scientists report that the opah manages to speed its metabolism and heat its body by flapping its fins. So, the opah can react and swim faster, says Nicholas Wegner, fisheries biologist of NOAA Fisheries’ Southwest Fisheries Science Center in La Jolla:
“Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments. 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.”
It’s necessary to add that other fish have developed regional endothermy, or limited warm-bloodedness. This feature makes them able to expand their reach from shallower waters into the colder depths.
But according to NOAA Fisheries, the opah’s evolutionary lineage suggests that it evolved its warming mechanisms in the cold depths, where the fish can remain with a consistent edge over other competitors and prey.
Moreover, it turns out that there are distinctive differences among opah from different parts of the world. Mr Wegner says that it’s quite interesting to compare warm-blooded features among them.
“Nature has a way of surprising us with clever strategies where you least expect them,” Wegner said. “It’s hard to stay warm when you’re surrounded by cold water but the opah has figured it out.”
Though, biologists still cannot be sure about the reasons for the increasing number of opah. Their population may be growing, or current conditions may be favoring. Despite the fact that opah are occasionally caught by local commercial fisheries, their rich meat has become popular in seafood markets.
“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.”