Effects of alarm cues on behavior and physiology of the sea cucumber Apostichopus japonicus

Alarm cues have an inevitable impact on organisms in aquaculture. The present study investigated the effects of alarm cues on the sea cucumber Apostichopus japonicus from behavioral and physiological perspectives. We found that the adhesion time significantly increased in sea cucumbers exposed to alarm cues (P = 0.008), indicating that sea cucumbers do not easily fall off the attachment substance into a harsh environment in seed production. Novelly, this present study clarified that fleeing response of sea cucumbers exposed to alarm cues was driven by tail movement rather than head movement. There was no significant difference in tentacle activity frequency (P = 0.705), indicating that alarm cues would not affect feeding behavior of sea cucumbers. In addition, there was also no significant difference in righting behavior of A. japonicus (P = 0.724), indicating that sea cucumbers probably respond to alarm cues through tube feet rather than tentacles or muscles. We reveal that alarm cues do not affect all but some the behaviors of sea cucumbers. Further, the present study found no significant difference in cortisol concentration (P = 0.583). In contrast, 5-hydroxytryptamine (5-HT) concentration significantly increased in sea cucumbers exposed to alarm cues (P = 0.004). These results suggest that the effect of alarm cues is probably mediated by 5-HT in sea cucumbers. Further, the present study found that the movement speed had a significant decrease in sea cucumbers fed with 3% dietary tryptophan when being exposed to alarm cues (P < 0.001). Thus, we suggest aqua-farmers feed 3% tryptophan to optimize behaviors of A. japonicus in seed production. In addition, the present study found that the artificial reef significantly shortened the righting response time of sea cucumbers (P = 0.002), indicating that artificial reefs are beneficial to righting behavior of sea cucumbers exposed to alarm cues. This present study provides new insights into behavioral and physiological reactions to alarm cues and into seed production of sea cucumbers.