The moonfish, also known as the opah, is the first known warm-blooded fish, it has been announced. This rather voluptuous fish warms its blood using a flapping motion with its pectoral fins, and maintains that heat it generates with “a series of counter-current heat exchangers within its gills”. The fish is found in deep sea waters around west Africa and Hawaii, and can grow to be several feet in size. As far as researchers know, this is the first fish of its kind.
According to the report, which was published in Science Mag, the fish’s warmed blood is pumped throughout its body, including to its heart, something that is said to offer “enhancing physiological performance and buffering internal organ function.”
The discovery started when NOAA researcher Nick Wegner was sent samples from the study’s co-author Owyn Snodgrass. It took Wegner a while to look at the samples, but when he did he said he “saw many structural similarities to the gills of other fast swimming fish…” That wasn’t the only thing he found, however.
When I cut open one of the gill arches, I noticed an incredible network of blood vessels, something I had never seen before in the gills. Something no one had ever seen before.
Those blood vessels serve as a sort of “counter-current” heat exchanger, warming the blood back up that’s coming back into the core of the fish’s body. That, combined with the flapping action of its fins, keeps the body temperature up.