Characteristics of the sleep structure in the cleaner wrasse Labroides dimidiatus.

Sleep is a widespread phenomenon among animals, yet its evolutionary traits and core functions remain largely enigmatic. To elucidate the fundamental characteristics of behavioral sleep in fish, we conducted quantitative assessments of behavioral and physiological properties, including body movement, eye movement, yawning, and ventilation, during sleep in the cleaner wrasse Labroides dimidiatus under laboratory conditions. The sleep states of the cleaner wrasse were characterized by a decreased ventilation rate, occasional distinctive waving movements, rapid eye movement (REM) episodes, and an increasing trend in both ventilation rate and REM episodes toward the end of the night period. Waving movements, temporal decreases in ventilation rate, and REM episodes showed distinct relationships. The patterns of behavioral and physiological features observed in the cleaner wrasse closely resemble those documented in mammals, leading us to propose that the structure of behavioral sleep is conserved across vertebrate species. Our findings further support the notion that the alternation of two  sleep states, Non-REM/slow-wave sleep and REM/paradoxical sleep, constitutes a shared sleep structure of sleep across a wide range of vertebrate species.