The study was published in the Nature journal Scientific Reports. It demonstrates how much more there is to learn about animals that have intrigued biologists for 200 years. “I’ve been fascinated by these fish for a long time,” UC associate professor Joshua Gross said. Cavefish evolved in caverns around the world. The species UC biologists examined, Astyanax mexicanus, diverged as recently as 20,000 years ago from surface fish still found in nearby streams in Sierra de El Abra, Mexico.