Sleeping with the fishes: Somalian cavefish shed light on our body clocks

Eyeless fish that have evolved underground, completely isolated from the day-night cycle, may offer clues to how our body clocks work up here on dry land. Authors of a report published today in the online journal PLoS Biology investigated a species of cavefish, Phreatichthys andruzzii, which has lived isolated for 2 million years beneath the Somalian desert. The report shows the cavefish has an unusual circadian clock: it ticks over an extremely long period (nearly two full days). This is despite the fish not having exposure to daylight, which is thought to be a key driver in terrestrial body clocks.