Effects of dietary Bacillus on foraging behavior, food consumption, digestive enzyme activity, and defecation outputs of the sea cucumber Apostichopus japonicus at low temperature: New insights into overwintering management

Abstract

Low efficiency is one of the most serious problems of sea cucumber (Apostichopus japonicus) seed production in winter. Probiotics as dietary supplements have the potential to address this problem. The aim of this study was to investigate the effects of the application of dietary Bacillus amyloliquefaciens and B. methylotrophicus on foraging behaviors, food consumption, digestive enzyme activity, and defecation outputs of small A. japonicus that were cultured in sea water at 5 °C for 12 days. We found that sea cucumbers supplemented with Bacillus showed significantly longer foraging distance (N = 6, P < 0.001), higher foraging success rate (N = 6, P = 0.016), shorter foraging time (N = 6, P = 0.006), and faster foraging speed (N = 6, P < 0.001), compared to the control group. In addition, food consumption (N = 9, P < 0.001), amylase (N = 3, P = 0.039) and protease enzyme (N = 3, P = 0.025) activities, and defecation outputs (N = 9, P = 0.04) of sea cucumbers fed with a diet supplemented with Bacillus were significantly higher than those of the control group. These results indicate that dietary Bacillus has great potential to increase the aquaculture productivity of sea cucumbers in winter. It is advisable to be an environmentally friendly solution to resolve the overwintering problems in A. japonicus aquaculture. The present study further enriches our understanding of the potential role of Bacillus and provides valuable information for its application at low temperature and new insights into the overwintering management for A. japonicus aquaculture.