The influence of sleep disruption on learning and memory in fish

Sleep is ubiquitous across animal taxa. Strong evolutionary pressures have conserved sleep over the evolutionary history of animals, yet our understanding of the functions of sleep still largely derives from mammals and select laboratory models. Sleep is considered to play an important role in mental processes, including learning and memory consolidation, but how widespread this relationship occurs across taxa remains unclear. Here, we test the impact of sleep disruption on the ability of the cleaner fish (Labroides dimidiatus) to both learn and then remember a novel cognitive task. We found a significant negative relationship between sleep disruption and the ability to learn a food reward choice system. Specifically, we found that fish in a disturbed sleep treatment took significantly longer and made more incorrect decisions when finding the food reward, compared to individuals in a non-disturbed/normal sleep treatment. In contrast, the differences between the two treatment groups were non-significant when fish where tasked with remembering the food reward several days later. Our results demonstrate a negative impact of sleep disruption on performance in a cognitive challenging task and that the effects were strongest when fish were first exposed to the challenge. Importantly, we show that the association between sleep and mental processes, such as learning, may be widespread across vertebrate taxa and potentially have an early origin in the evolutionary history of animals.