Fish that live in complete darkness and have lost their sight stay awake more than do sighted fish, probably because they need to spend more time feeding. Karen Hopkin reports.Creatures that live in the dark may lose their sight over evolutionary time. They may even lose their eyes entirely. Now it appears that they also lose sleep. Because a new study shows that cave-dwelling fish spend more time awake than their counterparts at the sunny surface. The finding is in the journal Current Biology.
Researchers studied three populations of Mexican tetra in the lab. Fish that live in creeks or rivers have two eyes and see just fine. But those that have adapted to living in caves lack eyes. What they do have is insomnia. The scientists observed that the tetras that normally spend time in the light do sleep soundly at night, resting on the bottom of their tanks. The cave fish, on the other hand, remain on high alert, patrolling their habitats even after hours.
The researchers are working to identify the genes responsible for this fishy restlessness. Not that they’ll reveal how you can get by on minimal shut-eye. Because the cave fish may not need less sleep—they may need to stay awake to forage more in an environment where food can be scarce and appear unpredictably. And even a blind fish can see: you snooze, you lose.
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