There’s nothing about the opah that says “fast-moving predator”. Tuna, sharks, and swordfish are fast-moving predators and accordingly, their bodies look like streamlined torpedoes. By contrast, the opah looks like a big startled frisbee, with thin red fins stuck on as an afterthought.

It’s pretty (silver body and red fins) and big (up to two metres long), but fast? Nicholas Wegner from the National Oceanic and Atmospheric Administration certainly didn’t think so when he first started studying it. Since then, he has discovered that the opah is an active predator, which has a trait that no other fish possesses.

It is warm-blooded.

Most fish have body temperatures that match the surrounding water. A small number of them can warm specific parts of their