Meet Opah. He is a fish that circulates heated blood throughout his body and likes to actively hunt in cold, deep, dimly lit waters. What does he eat you may ask? Hopefully not humans.
Researchers from the National Oceanic and Atmospheric Administration (NOAA) have just announced the discovery of the world’s first fully warm-blooded fish in a study published today, in the journal Science.
Dubbed “opah”, the fish circulates heated blood throughout its body by rapidly flapping its large, pectoral fins to move around. It’s not unlike how birds and bats use wings.
Heidi Dewar, paper author and researcher at NOAA’s Southwest Fisheries Science Center, admitted that scientist knew right from the start that the opah was special.
Most fish that live hundreds of feet below, in the darkest, coldest depths of the ocean, tend to be very slow in their movements due to the low, low temperatures. They simply set a trap and wait for food to come to them, rather than go out and actively hunt their prey.
Opah, on the other hand, has no such impairment. It moves swiftly in its natural habitat, actively chasing down quick-moving prey such as squid, can migrate long distances, and even shares many features generally associated with large, agile, active predators, such as a large heart, lots of muscle and big eyes.
It was Nicholas Wegner, lead study author and NOAA researcher, who first offered an explanation for the fish’s unusualness. By quickly and constantly flapping its wings, the fish generates heat, speeding up its metabolism, movements and reaction time.
The answer lies in the opah’s uniquely structured blood vessels. All species of fish have two types of blood vessels in their gills – the ones that carry blood in from the body to pick up oxygen, and the ones that carry oxygenated blood back out into the ocean.
The opah’s incoming blood is warm due to first circulating through its body. The opah’s outgoing blood is cold due to coming in contact with water in the fish’s gills. The two sets of blood vessels are engineered so that warm blood leaving the body core can heat up cold blood returning from the respiratory surface, allowing for warm blood to be delivered throughout the fish’s body. It’s a design known as “counter-current heat exchange”.
Wegner is very excited about the discovery and very fascinated by the species, proudly saying that “There has never been anything like this seen in a fish’s gills before. This is a cool innovation by these animals that gives them a competitive edge”.
Some other types of fish, such as tuna and sharks, have been known for their ability to warm up specific parts of their bodies, though the opah is the first known species to maintain an elevated temperature all throughout its body.
Test results showed that the tire-sized opah is capable of maintaining a core body temperature roughly 5 degrees Celsius warmer than that of the surrounding water it’s swimming in.
The discovery is not without controversy as Diego Bernal, an associate professor of biology at the University of Massachusetts Dartmouth, believes that despite all evidence, the opah is still a regional endotherm, just one than can keep larger region of its body warm.
He points out that the warmest areas in the opah’s body are the heart and the area around the eyes and brain, while the edges of its body are slightly colder.
Image Source: www.capitalotc.com