Researchers at New York University believe that the sleeping patterns of deep-water fish can possibly elicit a deeper understanding of sleeping disorders in humans.
The study published this month in Current Biology focuses on a species of cavefish, Astyanax mexicanus. This fish has genetically adapted to the stresses of living in an environment that is deep underwater and usually devoid of any light. One of their major genetic changes is their blindness; they have lost all eyesight and pigmentation in their eyes.
The researchers, headed by biologist Richard Borowsky, noticed that A. mexicanus remained relatively more active at night compared to another closely related species of fish that lives near the water’s surface and retains the ability to see.
Using three groups of fish that have become separated over their evolutionary history and a control group of their surface relatives, the researchers began to analyze the fishes’ sleep patterns.
Their first step was to determine which individual fish were asleep. They concluded that sleeping fish adopt a characteristic pose where they stop moving, drop their tails and fall to the bottom of the tank. Holding this pose for longer than 60 seconds was characterized as sleep. Waking the fish out of this state took three times as long as it did for fish who held the pose for less than 60 seconds.
Their results showed that while the cavefish slept an average of 110 to 125 minutes per day, surface fish averaged 800 minutes, almost seven times that of their bottom-dwelling relatives. Most importantly, the decrease in sleep held across all three groups of cavefish, suggesting a genetic cause of their insomnia.
The group’s next step is to investigate the relationship between genes and sleep behavior in humans. From there, the researchers hope to determine if there is a genetic predisposition for sleeping disorders such as insomnia.
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