Los Angeles - Fish might not have eyelids, but they do sleep, and some suffer from insomnia.

California scientists studying sleep disorders in humans found that some zebrafish, a common aquarium pet, have a mutant gene that disrupts their sleep patterns in a way similar to insomnia in humans.

Zebrafish with the mutant gene slept 30 percent less than fish without the mutation. When they finally drifted off they remained asleep half as long as the normal fish.

The mutant fish lacked a working receptor for hypocretin, a neuropeptide that is secreted in normal fish by neurons in the region of the brain that controls hunger, sex and other basic behaviors.

Zebrafish, also known as zebra danio, have become popular research subjects because they are cheaper to breed than mice and they have a backbone that better represents the human nervous system than fruit flies.
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