
Somalian cave fish (Phreatichthys andruzzii) evolved in the perpetual darkness of caves more than a million years ago. Even so, they have a working, albeit distorted, biological clock.
A blind cave fish that has spent millions of years underground isolated from evidence of day and night still has a working biological clock, albeit an unusually distorted one, scientists find.
This research could yield new clues on how such clocks might work in animals in general, researchers added.
Internal clocks known as circadian rhythms help animals, plants and other life to adapt their daily activities to the cycle of day and night. These clocks do not always follow a precise 24-hour schedule, so to keep synchronized with the natural world, they get reset on a daily basis by signals such as daylight.
One question circadian clocks bring to mind is whether and how those creatures that live in perpetual darkness still keep time. For instance, about 50 fish species worldwide have evolved to live without sunlight in caves, many times losing their eyes.
"Cave fish give us a unique opportunity to understand how profoundly sunlight has influenced our evolution," said researcher Cristiano Bertolucci, a chronobiologist at the University of Ferrara in Italy.













