Effects of stocking density on growth, behavior, digestion, and gut health of the sea cucumber Apostichopus japonicus: new insights into land-based aquaculture

Abstract

The increasing demand stimulates the rapid development of sea cucumber aquaculture industry in China. High stocking density is commonly used in the land-based aquaculture, but greatly affects the growth rate of sea cucumbers. In the present study, two different stocking densities were set to investigate the effects on growth, fitness-related behaviors, digestion, and gut health of the sea cucumber Apostichopus japonicus. We found that the terminal wet weight and weight gain rate significantly reduced in sea cucumbers at high stocking density. Feeding behavior significantly decreased in those at high stocking density, while crawling behavior was not affected. Protease activity was significantly inhibited in sea cucumbers at high stocking density. This may be an important reason for the reduced feeding behavior. Intestinal morphology showed that intestinal diameter, folds height, and enterocyte height significantly reduced in sea cucumbers at high stocking density. Degenerated intestinal structure is closely related to inhibited protease activity. Furthermore, the abundance of Proteobacteria increased, but the abundance of Bacteroidetes reduced in the gut of sea cucumbers at high stocking density. This result suggests that gut health was affected in sea cucumbers at high stocking density. In conclusion, reduced feeding behavior, degradation of intestinal structure, and changed intestinal microbial composition are important reasons affecting the growth of sea cucumbers. This finding provides valuable information for the high-density land-based aquaculture of A. japonicus.