Leighton Naylor is an English man. He has a pet fish. The fish is called Einstein, because why not? It's a pet. If I had a dog, it would be called Thorin, or Erwin, or something.
Einstein has a dysfunctional buoyancy bladder (mostly known as swim bladder) which is the organ that allows fish to go up and down in the water. It's a tiny vessel surrounded by muscles: muscles tighten, it gets smaller and the fish sinks; muscles relax, it gets larger and the fish floats. Like a submarine, but tiny and adorable.
So Einstein was ill. He would sink to the bottom of the tank, and that's sad. A fish that can't swim? Oh, the humiliation!
Sometimes these disorders are caused by bad nutrition, but apparently that wasn't the cause.
That's when Leighton made a life vest for Einstein:
Those are empty plastic tubes, and they help Einstein float.
Einstein's motion is still very constrained, requiring manual feeding and all. But hey, he can swim now!
And that is how science made a swimless fish swim again. Thank you, science!
*Dante Sheperd made this nice sign.