Toxic effect of chronic nitrite exposure on growth and health in Pacific white shrimp Litopenaeus vannamei

Abstract

Juveniles of the Pacific white shrimp Litopenaeus vannamei were exposed to 0 (control), 2, 6.67, and 20 mg L−1 nitrite-N for 30 days, and the growth, immunity, and gut microbiota were evaluated. The weight gain of shrimp exposed to 20 mg L−1 nitrite-N was significantly lower than that in the control. Antioxidant capacity, measured as superoxide dismutase and glutathione peroxidase activities, catalase expression, and malondialdehyde content, was not affected by chronic nitrite-N exposure. The expressions of immune related genes (IMD and Toll) in shrimp exposed to 20 mg L−1 nitrite-N were significantly higher than that in shrimp exposed to 2 mg L−1 nitrite-N, but no differences were found with the control. Regardless of nitrite-N exposure concentrations, Bacteroidetes, Proteobacteria, and Actinobacteria were the dominant phyla in the gut of L. vannamei. With the increase of nitrite-N concentration, the diversity of gut microbiota increased in L. vannamei. The relative abundance of opportunistic pathogens, such as Pseudoalteromonadaceae and Vibrionaceae, increased in shrimp exposed to 20 mg L−1 nitrite-N. The relative abundance of denitrifying bacteria increased in shrimp exposed to 2 mg L−1 nitrite-N, but decreased in those exposed to 6.67 or 20 mg L−1 nitrite-N relative to those in the control. The predicted microbial-mediated functions showed that pathways for digestive function and metabolic capacity were significantly inhibited. All findings in this study indicate that L.vannamei can deal with the stress caused by nitrite-N within levels lower than 6.67 mg L−1, but chronic exposure to a high concentration (> 6.67 mg L−1) would reduce shrimp growth and alter its immune system by destroying gut microbiota homeostasis.