Differences in feeding behavior and intestinal microbiota may relate to different growth rates of sea cucumbers (Apostichopus japonicus)

The sea cucumber Apostichopus japonicus is an economically important species in Asia. Large growth differences have been recorded for A. japonicus during field surveys and culture practices. These growth differences can seriously impact the recovery of wild populations and breeding efficiencies in aquaculture systems. This study explored differences in movement behavior, feeding behavior, digestive ability and intestinal microbes of A. japonicus that displayed obvious differences in growth under the same culture conditions. The results showed that there was no significant difference in the movement behavior of A. japonicus with different growth rates, but the feeding behavior of slow-growing A. japonicus was significantly reduced. The activity of trypsin, the main digestive enzyme in A. japonicus, was significantly decreased in slow-growing individuals. There was a marked variation in the gut microbiota composition of sea cucumbers with different growth rates. Compared with slowgrowing A. japonicus, fast-growing A. japonicus had a higher alpha diversity, and abundance of Rhodobacteraceae, Rubritaleaceae, and Pirellulaceae. Many of these bacteria were related to the algal polysaccharide degradation. However, the abundance of Vibrionaceae and Burkholderiaceae was higher in slow-growing A. japonicus, which contained potential pathogenic bacteria. This indicated the differences in feeding behavior, digestive ability and intestinal microbiota was related to different growth rates of A. japonicus. These differences will continue to promote growth differences over time. This research provided new insights for understanding the large growth differences in A. japonicus.