Promotion of pellet-feed feeding in mandarin fish (Siniperca chuatsi) by Bdellovibrio bacteriovorus is influenced by immune and intestinal flora

Abstract The feeding preference of the mandarin fish, Siniperca chuatsi, for live bait fish over pellet feed increases the costs and risks of breeding. Animal feeding behavior is directly or indirectly influenced by intestinal flora and innate immunity. Probiotics have been shown to regulate intestinal flora and stimulate innate immunity in a variety of species. In this study, during the pellet-feed feeding process of mandarin fish, Bdellovibrio bacteriovorus at a concentration of 108 PFU (plaque forming unit)/mL was added to the water body for 6 weeks, and the effects on the survival, growth, appetite, intestinal flora, innate immunity, antioxidant capacity, and intestinal histology of mandarin fish were studied. The results showed that addition of B. bacteriovorus at a concentration of 108 PFU/mL to aquaculture water could significantly promote mandarin fish pellet-feed feeding, improve the survival rate and growth performance of mandarin fish that were fed pellet feed. Compared with the control group, addition of B. bacteriovorus promoted the expression of appetite-regulating genes nerve peptide Y (Npy) and agouti gene-related protein (Agrp). Intestinal microflora analysis and intestinal histological analysis results revealed that B. bacteriovorus reduce the abundance of pathogenic bacteria Aeromonas in the intestinal flora, reduce damage to the intestinal mucosa and epithelial cells, and increase the thickness of the intestinal basement membrane and height of intestinal villi. Similarly, an increase in the serum lysozyme and immunoglobulin M (IgM) contents was observed after B. bacteriovorus administration. Moreover, B. bacteriovorus improved the activity of antioxidant enzymes, reduced glutathione (GSH) and catalase (CAT). In general, addition of B. bacteriovorus at a concentration of 108 PFU/mL to aquaculture water could significantly promote pellet-feed feeding of mandarin fish and improve the growth performance and survival rates of mandarin fish under pellet-feed feeding conditions. This promoting effect may be achieved by B. bacteriovorus stimulation of innate immunity and regulation of intestinal flora.