If you don’t know what the difference between warm-blooded and cold-blooded is, that’s ok. For some of us, school was a very long time ago. Generally, fish are cold blooded. Lizards and other reptiles are, too. All mammals are warm blooded (whales included, even though they live in the ocean). A fish’s temperature matches the water it is in, and they don’t have the ability to warm themselves up.

Except for this guy:

That’s an opah fish, and it’s just been discovered to be the first warm-blooded fish out there.

[The opah’s] whole body is usually about five degrees Celsius warmer than the water it’s swimming in.

A biologist at the National Oceanic and Atmospheric Administration, Nicholas Wegner, told Science that the discovery was an “accident”. Speaking to National Geographic, he explained their findings:

His team caught some opah during a research trip, and subsequently decided to find out more about the species. During a dissection, Wegner noticed that the gills were sporting the same kind of blue and red blood vessels, called retia mirabilia, that tuna and sharks use to heat parts of their bodies. Except that unlike sharks and tuna, the opah’s red and blue blood vessels were located inside the gills, rather than in the fish’s swimming muscles.

If you thought that was quite scientific for a Friday, wait for this:

The finding means that when the opah flaps its pectoral fins to generate heat, warm blood gets to travel through the entire body before being cooled by water in the gills. When that happens, the cold blood in the gills — blood that’s now also oxygen-rich because of the exchange with water — gets heated by oxygen-depleted, warm blood coming from the body. Thus, cold blood never gets to exit the gills.

I know. Someone would have to draw a very colourful diagram for me to get that (biology was not a strong point for me at school). But, exciting times for the animal world. Is this a bit of evolution?

[Source: The Verge]