The hybrid abalone Haliotis discus hannai female x H. fulgens male (DF) shows obvious growth advantages compared with one of its parents, H. discus hannai (DD); however, the reasons for these advantages are not fully understood. Using a video surveillance system, the current study showed that the feeding behaviors of DD and DF exhibited an obvious circadian rhythm, with significantly more feeding at night by DD and DF than during the day. In addition, the amount of time feeding by DF during the day and at night was significantly higher compared with that of DD, especially at ZT8 (20:00), ZT12 (24:00), ZT16 (04:00), and ZT20 (08:00), with the proportion of time feeding by DF increasing 2.22-, 1.60-, 2.71-, and 2.40-fold compared with those of DD, respectively. The maximum values of pepsase activity in DD and DF, of alpha-amylase activity in DD, and of alginate lyase activity in DF coincided with the peak feeding period. Relative to the changes in expression levels of neuropeptide Y receptor (NPYR) in the intestine, diurnal changes in NPYR expression levels in cerebral ganglia were consistent with the changes in feeding behavior, being highest at 24:00 h in both DD and DF and then declining. There was no significant difference in the circadian expression levels of cholecystokinin receptor (CCKR) in the cerebral ganglia, whereas, in the intestinal tract, peak CCKR expression levels coincided with its anorexigenic effect; the expression levels of CCKR in the intestinal tract exhibited a significant circadian rhythm in DD. These results explain the growth advantage of DF over DD in terms of feeding behavior and digestive physiology, and support the hypothesis that diurnal changes in feeding-related genes in the nervous and digestive systems are correlated with the initiation of abalone feeding behavior. Our findings also provide guidance for developing a suitable feeding strategy for, and improving the efficiency of, the production of abalone.
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