Potosi Pupfish Cyprinodon alvarezi

The Potosi Pupfish (Perrito de Potosi") was endemic to only one large, clear spring-fed pool near El Potosi in northeast Mexico. Sadly it and the Catarina Pupfish, Megupsilon aporus, and a crayfish from the same pool are all now extinct in the wild following human drainage of the pool for irrigation from 1984 to the 1990s.

The Catarina Pupfish became totally extinct in 2015 but a few Potosi Pupfish survive in captivity in a North American and a British aquarium. The breeding male, above left, has beautiful milky white irridescent scales and a thick black border to the tail fin. They grow to 5-6cm long.