FISH might not have eyelids, but they do sleep, and some suffer from insomnia, scientists reported Monday.

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 researchers at the Stanford University School of Medicine said.

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.

The researchers, led by Emmanuel Mignot, said they would look for fish that have a mutation that causes them to oversleep or never sleep in the hope of discovering if sleep-regulating molecules and brain networks developed through evolution.

“Many people ask the questions, ‘Why are we sleeping?’ and, ‘What is the function of sleep?’” Mignot said. “I think it is more important to figure out first how the brain produces and regulates sleep.” <2001>(SD-Agencies)