It began more than two decades ago in Teuchitlán, a town near the Tequila volcano. A half-dozen students, among them Omar Domínguez, began to worry about the little fish that fit in the palm of a hand and had only ever been seen in the Teuchitlán river. It had vanished from local waters, apparently due to pollution, human activities and the introduction of non-native species.

Domínguez, now a 47-year-old researcher at the University of Michoacán, says that then only the elderly remembered the fish called “gallito” or “little rooster” because of its orange tail.