Effects of photoperiod on feeding, gut microbiota and growth of razor clam Sinonovacula constricta

In the present study, we aimed to explore the effects of photoperiod on the feeding, gut microbiota and growth of razor clam Sinonovacula constricta , and to ascertain the optimal feeding period based on the most favorable photoperiod. Five photoperiod groups (12D:12 L, 14D:10 L, 16D:8 L, 18D:6 L, 20D:4 L) and four zeitgeber time points (ZT0/08:00, ZT6/14:00, ZT12/20:00, ZT18/02:00) were set, and the oxygen consumption, ammonia excretion, feeding rate, digestive enzyme activities (α-Amylase, Pepsin and Lipase) and related gene ( AMS , PEP , LPS ) expression patterns, gut microbiota and growth performances were analyzed. The results showed that the feeding rate was higher under short-day photoperiods (16D:8 L, 18D:6 L, 20D:4 L) than long-day photoperiods (12D:12 L, 14D:10 L), but the digestive enzyme activity and related gene expression levels were higher under 16D:8 L and 18D:6 L than 20D:4 L. In the growth experiment, the razor clams exhibited significantly higher shell length growth rate, weight gain rate and specific growth rate under the 18D:6 L photoperiod compared to other photoperiods ( P < 0.05). The results of 16S rRNA gene amplicon sequencing showed that the gut microbiota diversity and growth-related microbial flora abundance were higher under 18D:6 L. According to the data of different light and dark periods under 18D:6 L, the oxygen consumption and ammonia excretion rates, feeding rate, digestive enzyme activities and gene expression levels were all higher at ZT12–20 (20:00–4:00) compared with other time periods. Collectively, these results suggested that the photoperiod 18D:6 L may facilitate the feeding, digestion, metabolism and promote the growth, and increasing the food supply at 20:00–4:00 during night can further promote growth of razor clams. • The 18D:6 L photoperiod is more conducive to feeding and digestion of razor clams. • The probiotic bacterium Neptunomonas abundance of gut was higher at night than during the day. • The young razor clams grew faster under the 18D:6 L photoperiod. • Increasing the food supply during nighttime 20:00–4:00 can promote growth of razor clams.