Contradicting everything we previously knew about basic biology, scientists have come across the first ever warm blooded fish. The opah, or by its scientific name, the Lampris guttatus, is a large fish capable of independently maintaining a high body temperature.
The paper, published on Thursday in the journal Science reveals this curious zoological mystery.
According to basic biology facts we are all acquainted with, reptiles, amphibians and fish are cold blooded- which means that they cannot maintain a high body temperature. It’s only birds and mammals that are capable of regulating their temperatures.
Defying all the previously known theories, the opah fish uses a curious yet remarkable mechanism to remain warm. This predatory fish’s gills contain particular types of blood vessels constantly circulating warm blood.
In the deep vastness of the Earth’s oceans, a warm-blooded fish would clearly have a tremendous advantage over other brethren.
Cold, dark waters make fish sluggish and slow. Even predatory fish are slow-moving, awaiting to surprise their prey rather than chasing it down.
Warm blooded creatures aren’t limited by the low water temperatures, though. And while seals and whales are capable of exploiting this speed and agility bonus. Thick layers of fat work as insulation for these animals capable of swiftly snatching live food.
But until recently, scientists had believed that fish aren’t capable of such temperature regulatory mechanisms because of their breathing patterns.
More specifically, because of the fact that they use gills in order to directly extract oxygen molecules from the water they swim in. Though there are undeniable advantages to this evolutionary solution (remaining underwired indefinitely as opposed to whales or seals who need to repeatedly come up for air), there are also disadvantages.
Muscle activity is an essential warmth producing mechanism but when it comes to fish, even when blood is warmed via muscle contractions, it leaves the heart and travels directly to the gills where it is immediately cooled.
Here is where the opah fish shines in a unique light. The opah has a large heart compared to other predatory fish living in the same waters. But its gill vascularization is what sets it apart.
When studying gill samples from the opah fish, Nicholas Wegner noticed two distinct types of blood vessels. One set of vessels brings oxygen-poor blood from the body to the gills. The other, oxygenated blood to the body.
Incoming blood is warm because of the fish’s massive muscular activity. Outgoing blood, however, is cold after coming in contact with the water. The curious thing is that, in the case of the opah fish, these two distinct sets of blood vessels are so neatly packed together that incoming blood is capable of transferring its heat to outgoing blood before it goes into the body.
Scientists explain that this “counter-current heat exchange” is responsible for the opah’s warm blood.
Due to this unique mechanism, opah fish have a 5°C higher body temperature than the surrounding water and are capable of diving half a kilometer below the water’s surface without experiencing temperature shifts.
Opah fish aren’t that unknown: in fact, the fish is a favorite in restaurants and markets. However, its temperature had never before been an issue.
Because just certain organs and body regions are provided with warm blood, the term “regional endothermy” best suits the fish’s unique characteristics.
Image Source: Live Science
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