It has been a breakthrough discovery in the world of Ichthyology and biology fields alike. Previously believed that all fish were cold-blooded. A recent study has found that there is an exception. The Opah.
Lampris Guttatus or more commonly known as ‘Opah’ has recently been recognized as the first entirely warm blooded species of fish known to man. The Opah is disc shaped and laterally compressed (meaning its flat). They exhibit bright orange fins, a slightly less orange body and white speckles all over. These stunning critters can obtain lengths of up to 2m and a weight of about 250kg. They are distributed globally and stay in Tropical and Temperate waters at depths between 200m – 1000m. Opah typically feed on Squid, Krill and small fish.
Most fish are considered to be ectothermic, in simpler terms it means that their body temperature is equal to that of their surrounding environment. The reason for this is that when blood moves through the gills to collect oxygen, it comes in close proximity to the water passing over the gills. Thus, cooling and making the body temperature of the fish similar to that of its surroundings. There are some species that can heat up only certain areas and not their entire body. Sharks and Tunas have an increased temperature in the muscles that allow them to control the caudal fin, which helps to chase prey or flee from predators. While Billfish are able to raise the temperature of their eyes and brains to improve their sense of vision while hunting.
What makes the Opah so interesting is that its physiological features are not common to fish found in the Mesopelagic Zone (200m – 1000m) but rather similar to those that feed in much shallower depths. Due to this physiological phenomenon, it allows the Opah to be a highly active predator and hunt faster moving prey in deeper water. Unlike the other species of that depth, which are usually bottom feeders and have a flat body shape (opposite to that of the Opah) to help them feed off the bottom.
Contrary to its fellow comrades of the deep, the Opah has warm blood circulating its whole body, instead of certain areas. This is achieved by the continuous and vigorous movement of its pectoral fins and the unique positioning of blood vessels throughout the body. The vessels are very closely positioned to one other, which act like heat exchangers and allow for heat to be transferred to vessels that contain cooler blood coming from the gills. This warm oxygenated blood then leaves for the rest of the body, making it warm blooded.
One can only hope this recent discovery does not lead this beautiful creature into over exploitation. In recent years, the Opah has become quite popular for recreational anglers in the United States and as well as the sushi industry across the world. Once considered by-catch and poor quality meat, the Opah has recently been coined as restaurant quality. Due to its high fat content and rich red flesh, it is considered a prized fish for sushi restaurants around the world.