LAUSR

Summary The present study was conducted to evaluate the effects of different dietary chitosan oligosaccharide (COS) levels on digestive enzyme activity, intestinal bacteria flora, and growth performance of the tiger puffer (Takifugu rubripes). Some 600 fish (initial body weight 129.2 ± 3.1 g) were randomly allocated into twelve 2,000-L blue cylinder aquaria with 1,500-L of sea water and divided into four groups (n = 3 aquaria/diet). The fish were fed experimental diets supplemented with different levels of COS (0% [control, L1], 0.05% [LC1], 0.1% [LC2], and 0.2% [LC3]) for 8 weeks. During the experiment, the water temperature was 18 ± 1°C, salinity 28 ± 0.1, pH 8.0 ± 0.1 (mean ± SD, n = 672); airstones were positioned at the bottom of the tank, dissolved oxygen content was above 7.0 mg/L, with a photoperiod of 12 hr light: 12 hr dark. The results showed that dietary COS significantly increased growth performance, intestinal-somatic index (ISI), and intestinal protease as well as lipase activity (p   .05). High-throughput sequencing analysis showed that COS affected the richness and diversity of intestinal microbial species. The Shannon index of intestinal bacterial flora was significantly higher in the control group than in other groups (p < .05). However, dietary COS supplementation did not alter the phyla species of intestinal bacterial flora. There were significantly more Aliivibrio and Bacillus in LC3 than in other groups, and there were significantly fewer Faecalibacterium, Escherichia, and Bacteroides than in other groups at the genus level (p < .05). It can be concluded that dietary COS can improve the growth performance and intestinal digestive enzyme activity and alter the intestinal bacterial flora in the tiger puffer, Takifugu rubripes.