We were taught when we were in chool that humans and animals are warm-blooded , and fish, reptiles and amphipians are cold-blooded creatures.
However, scientists have now made the amazing discovery that one kind of fish is actually warm-blooded !
This fish, called the Opah, or Moonfish, lives in the cold depths of the ocean. Most fish that live in that cold of water are very slow moving because they get so cold that their heart does not work right.
You might have seen this effect if you have goldfish, and the bowl got too cold during the winter and the fish could barely move. Then , when you put them in a warmer room; they warmed back up and started swimming around again.
The Opah swims by moving its fins very fast, which keeps the blood circulating faster and generates heat in the fish's body. They also have two sets of gills, so that the warmer blood can help heat up the cold blood from the gills and it enters the Opah's body at a warmer temperature.
They are pretty large fish; so we won't likely be having one in our aquariums soon; but just knowing that such a thing as a warm-blooded fish actually exists is pretty interesting.