Effect of Pseudomonas stutzeri F2 on rearing water quality and growth, innate immunity, visceral morphology and gut microbiota structure of juvenile spotted seabass (Lateolabrax maculatus)

Abstract

Previous reports on the effects of probiotics on farmed fish have focused more on dietary supplementation, and this study evaluated the effects of Pseudomonas stutzeri F2 supplementation in rearing water on juvenile spotted seabass (Lateolabrax maculatus). Different from the control group (T0), where ammonia nitrogen levels were reduced by water exchange in the circulation system, the T1 and T2 groups supplemented the rearing water with low (3.0 × 103 CFU/mL) and high (3.0 × 105 CFU/mL) concentrations of P. stutzeri F2 with the ability to remove ammonia nitrogen and nitrite, respectively. After 33 d of rearing, the weight gain rate, specific growth rate, feed utilization and survival rate of the experimental group of spotted seabass were significantly improved (p < 0.05). P. stutzeri F2 activated superoxide dismutase (SOD), lysozyme (LZM) and catalase (CAT) activities in the serum of the experimental group of spotted seabass; increased glutathione peroxidase (GSH-Px) activity in the liver while decreasing malondialdehyde (MDA) levels. Microscopic observation of tissue sections revealed significantly improved muscle thickness and mucosal fold height in the T2 group of the midgut. The study of changes in the gut microbiota of spotted seabass by 16 S rRNA gene sequencing revealed a significant decline in the relative abundance of Proteobacteria (phylum) and Photobacterium (genus) in the P. stutzeri F2 supplemented groups. Aeromonas veronii challenge test to assess the disease resistance of spotted seabass found that the survival rate of the T2 group was the highest. Our study showed that the supplementation of P. stutzeri F2 with 3.0 × 105 CFU/mL in the rearing water increased the growth performance of spotted seabass, activated innate immunity, improved the relative abundance of gut microbiota, and enhanced resistance to A. veronii, providing a new idea for the application of probiotics.