In a recently published report, scientists from the National Oceanic and Atmospheric Administration (NOAA) explained how a newly-found fish defies everything we learned in school about fish being cold-blooded. Opah is the only fish discovered by man that has warm blood.
In their paper, scientists explain that the opah has a set of blood vessels in its gills that allow its body to keep a high temperature even at deepest and coldest places where it usually stays when looking for prey.
Also, the opah puzzles biologists with its odd deep sea hunting techniques. Usually, fish that lurk at abyssal depths are cold-blooded and do not usually engage in active hunting. They rather stalk their prey and display really sluggish moves.
Instead, the opah chases its prey down, is very quick moving, and has an entire equipment to match its peculiar hunting strategies which burn a lot of energy at those deep places. That equipment involves a larger heart, more muscles and enhanced vision.
NOAA researchers found how the world’s first warm-blooded fish was able to maintain a high body temperature. They think that the odd creature uses a unique method of swimming that generates a lot of heat.
While most fish undulate their bodies to propel themselves through water, the opah quickly flaps its fins to move in its environment. The resulted energy warms the blood in its vessels, while a unique set of gills further contribute to maintaining its body warm through a phenomenon known as “counter-current heat exchange.”
Tuna fish also have a similar set of blood vessels, which can only partially keep the fish warm. Tuna have only some organs and muscles that are kept particularly warm while swimming including their eyes and liver.
However, the opah is the only fish that have a set of gills that prevent the loss of body heat into the surrounding cold environment like most fish do. Researchers learned that the fish can keep its whole body warm at roughly 5 degrees above the temperature of the water they swim in.
Still, there are some scientists that believe that calling the opah a fully warm-blooded fish is inaccurate. They explain that this fish is just partially warming up his body just like tuna do, but it is a lot better adapted in retaining heat.
Diego Bernal argued that the opah has only a warm core within its body, but its extremities such as tail or outer regions remain cold. Even NOAA researchers admitted that the opah is warmer around its heart, brains and eyes, but the rest gets a little chillier.
Kathryn Dickson, one of the NOAA researchers admitted that Prof. Bernal may be right and the term “warm-blooded” a little outdated. She said that the rest of the fish’s body remain below the surrounding water’s temperature.
Image Source: DNA Barcoding
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