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 ____1____ at the sunny surface. The finding is in the journal Current Biology.

Researchers studied ____2____ 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 ____3____. 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, ____4____, 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 ____5____. And even a blind fish can see: you snooze, you lose.
【视听版科学小组荣誉出品】
counterparts three populations of insomnia remain on high alert unpredictably
在黑暗中生活的动物可能会在进化过程中失去视力，甚至可能一点东西都看不见。但现在发现，它们有可能连睡眠都失去了，因为一项新研究发现，和住在光照充足的浅层同伴相比，住在穴居鱼会更常保持清醒。这项发现刊登在《当代生物学》杂志上。 研究人员在实验室研究了三种墨西哥丽脂鲤种群。在溪里或河里生活的鱼有两只眼睛，视力良好。但穴居鱼则没有眼睛，而且患有失眠症。科学家观察发现，接触阳光时长正常的鱼类在晚上会在鱼缸底部睡得很安稳。而另一方面，穴居鱼仍然保持高度警惕，三更半夜还在居住的地方游来游去。 研究人员旨在鉴别使鱼类失眠的基因，而并不是说想展示如何在最小睡眠的状态下活下去。因为穴居鱼可能并不需要睡得更少——它们可能需要保持清醒，以便更经常地在食物短缺和食物不常出现的环境中觅食。一条瞎眼鱼都可以预见到：打个盹，你就亏了。