Effect of water temperature on diel feeding, locomotion behaviour and digestive physiology in the sea cucumber Apostichopus japonicus

This study used controlled laboratory conditions to directly assess the role of water temperature in controlling diel feeding and locomotion behaviours, and digestive physiology, in the sea cucumber Apostichopus japonicus. The results revealed that both the proportion of feeding individuals and ingestion rate were highest at 16 degrees C. Regardless of water temperature, sea cucumbers appeared to be nocturnal and their peak feeding activity occurred at 00:00 h to 04:00 h. Tentacle insertion rate was not significantly correlated with water temperature (<24 degrees C). In all temperature treatments except 24 degrees C, the proportion of moving sea cucumbers was also observed to be higher at night than during the day. The water temperature above thermal threshold (24 degrees C) for aestivation may alter the diel locomotion rhythm. The highest lipase and amylase activities were both observed at 20 degrees C. The highest activities of lipase and amylase at all temperature treatments were observed at 22:00 h to 02:00 h, which was slightly earlier than the feeding peak. In conclusion, even in total darkness, A. japonicus showed more active feeding and moving activities, and higher digestive enzyme activities, at night than during the day. These results demonstrated that diel feeding and locomotion behaviours, at least in the short term, were not controlled by light or low water temperature (<24 degrees C) but by an endogenous rhythm, and A. japonicus had the ability to optimize the digestive function for the coming feeding peak. These findings should provide valuable information for the development of the aquaculture of this species.