our science correspondent victoria gill reports. a little known species with an extraordinary story. the tequila fish is a small freshwater fish that lives in the rivers and lakes of south west mexico, but it s been missing, presumed extinct, for more than a decade. and it s just one of thousands of aquatic creatures that are facing extinction, but have slipped under the radar. small little things, a bit silver sometimes, a bit of colour when they breed, but not much interest on the global conservation aspect. now, with the help of conservationists at chester zoo, scientists in mexico have reversed that extinction, bringing captive bred fish back to the wild. the team has now confirmed that the fish are breeding, and that the population is recovering here. they re doing well. they started with the introduction of 1500 animals, so now we re about from 1500 individuals now, to tens of thousands, and now what we re seeing is that the species is slowly start expanding to the river system,