From Scientific American:
Fish might not have eyelids, but they do sleep, and some suffer from insomnia, scientists reported on 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 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.