Effects of chronic nitrate exposure on the intestinal morphology, immune status, barrier function, and microbiota of juvenile turbot (Scophthalmus maximus)

• Published in: Ecotoxicology and Environmental Safety
• Main Authors: Yu, Jiachen, Wang, Yanfeng, Xiao, Yongshuang, Li, Xian, Xu, Xiaojie, Zhao, Haixia, Wu, Lele, Li, Jun
• Format: Report
• Language: English
• Published: ACADEMIC PRESS INC ELSEVIER SCIENCE 2021
• Subjects: Scophthalmus maximus; Nitrate exposure; Intestinal health condition; Intestinal microbiota; Environmental Sciences & Ecology; Toxicology; Environmental Sciences; Turbot
• Online Access: http://ir.qdio.ac.cn/handle/337002/169309; http://ir.qdio.ac.cn/handle/337002/169310; https://doi.org/10.1016/j.ecoenv.2020.111287

Coming along with high water reuse in sustainable and intensive recirculating aquaculture systems (RASs), the waste products of fish in rearing water is continuously accumulated. Nitrate, the final product of biological nitrification processes, which may cause aquatic toxicity to fish in different degrees when exposed for a long time. Therefore, the present study was conducted to evaluate the impact of chronic nitrate exposure on intestinal morphology, immune status, barrier function, and microbiota of juvenile turbot. For that, groups of juvenile turbot were exposed to 0 (control check, CK), 50 (low nitrate, L), 200 (medium nitrate, M), and 400 (high nitrate, H) mg L-1 nitrate-N in small-sized recirculating aquaculture systems. After the 60-day experiment period, we found that exposure to a high concentration of nitrate-N caused obvious pathological damages to the intestine; for instance, atrophy of intestinal microvilli and necrosis in the lamina propria. Quantitative real-time PCR analysis revealed a significant downregulation of the barrier forming tight junction genes like occludin, claudin-like etc. under H treatment (P < 0.05). Intestinal MUC-2 expression also decreased significantly in the nitrate treatment groups compared to that in the control (P < 0.05). Additionally, the expression of HSP70 and HSP90 heat-shock proteins, toll-like receptor-3 (TLR-3), interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) significantly increased (P < 0.05), whereas that of transforming growth factor-beta (TGF-beta), lysozyme (LYS), and insulin-like growth factor-I (IGF-I) significantly decreased with H treatment (P < 0.05). The results also revealed that intestinal microbial community was changed following nitrate exposure and could alter the alpha-diversity and beta-diversity. Specifically, the proportion of intrinsic flora decreased, whereas that of the potential pathogens significantly increased with M and H treatments (P < 0.05). In conclusion, chronic nitrate exposure could ...