Image: Branding Pot / shutterstock.com This video shows the weirdness of the Devils Hole pupfish. Deep inside a single limestone cavern in Nevada's Mojave Desert lives one of the rarest fish on Earth. The tiny, shimmering blue fish can be found in only one known natural habitat in the world: a water-filled limestone fissure called Devils Hole. That's the only place on the planet where they live in the wild today. Devils Hole is physically separated from any other aquatic system. It's a vertical rock chamber opening into warm, mineral-rich groundwater. Think of it as a secret little swimming pool carved into the earth, except nothing else lives in it but these fish. These pupfish survive in water that stays around 93°F (34°C), with extremely low nutrient availability and almost no seasonal variation. They've adapted to conditions that would kill most fish. They're the ultimate homebodies, having essentially committed to living their entire existence in a single, sunlit crack in the ground.…