The known population of one of the world's rarest fish has just doubled, thanks to a lucky find in the waters off Tasmania, Australia.Meet the red handfish, a name that reflects the hand-shaped fins on the sides of its body. The striking creature doesn't really swim — it "walks" slowly along the seafloor. And until recently, researchers say they were aware of only one colony of the rare animals, with around 20 to 40 fish.A team of seven divers from Australia's Institute for Marine and Antarctic Studies and the Reef Life Survey heard reports that a red handfish was seen in another area and went down to investigate.After two days of fruitless searching, they were about to call the mission off when IMAS technical officer Antonia Cooper spied a red bottom-dweller."I was halfheartedly flicking algae around and, lo and behold, found a red handfish," she says in an IMAS video. "Once we found that first one, I signaled to the other divers that we had a sighting, which meant we could then focus our search area to that same spot. And sure enough, in a 50-meter-by-20-meter area, we discovered another eight fish."The scientists think that the new colony has another 20 to 40 fish. And it's "a number of kilometers away" from the other known group. Because handfish move so slowly, that suggests that they are genetically distinct."It means there's potentially a bigger gene pool and also that there are potentially other populations out there that we're yet to find, so it's very exciting indeed," Cooper said.The species has recently gone through a "marked decline," according to the Australian government. It is believed to rely on green algae as a place to spawn, and that environment is being degraded because of an increase in a sea urchin population that grazes on the algae. Rising water temperatures are also threatening this species and many others.National Geographic details other factors impacting the fish: