Project description:The circadian rhythm is the most general and important rhythm in biological organisms. In this study, continuous 24 h video recordings showed that the cumulative movement distance and duration of the abalone, Haliotis discus hannai reached their maximum values between 20:00–00:00, but both were significantly lower between 08:00–12:00 than at any other time of day or night (P < 0.05). To investigate the causes of these diel differences in abalone movement behavior, their cerebral ganglia were harvested at 00:00 (group D) and 12:00 (group L) to screen for differentially expressed proteins using tandem mass tagging (TMT) quantitative proteomics. Seventy-five significantly different proteins were identified in group D vs. group L. Acetylcholinesterase (AChE) was found three times, and its expression levels differed significantly between day and night (P < 0.05). A cosine rhythm analysis found that the concentration of acetylcholine (Ach) and the expression levels of AchE tended to be low during the day and high at night, and high during the day and low at night, respectively.