Using these techniques, the researchers found many differences in the cave fish genomes compared with their surface fish relatives', including a deleted DNA segment in the gene hpdb. GENETICS Astyanax mexicanus cave fish have adapted to an incredibly tough environment: chilly, pitch-dark caves that flood about once a year, providing brief feasts separated by long periods of starvation. Previous cave fish studies have connected pigment loss to increased levels of these hormones and to the cave fish's low sleep requirements. [Extracted from the article]