Exposure to environmentally relevant concentrations of deltamethrin renders the Chinese rare minnow (Gobiocypris rarus) vulnerable to Pseudomonas fluorescens infection.

Abstract

In this study, to assess the immunotoxicity of deltamethrin on fish, adult Chinese rare minnows (Gobiocypris rarus) were exposed to 0.1, 0.3, and 1μg/L deltamethrin for 28 d. Many immunological parameters and histopathological alterations were determined. The results showed that lymphocyte number was markedly decreased at 0.3 and 1μg/L treatments, whereas the neutrophil number was strongly increased at 1μg/L treatments (p<0.05). Furthermore, lysozyme (LYS), immunoglobulin M (IgM), and complement component 3 (C3) levels at 0.3 and 1μg/L treatments were markedly reduced, whereas alkaline phosphatase (ALP) activity were marked increased at 1μg/L treatments (p<0.05). The transcripts of almost all TLR (Toll-like receptor) signaling pathway-related genes were up-regulated. Histological lesions in the livers, intestines, and gills were observed at all treatments. Then, all remaining fish from controls and deltamethrin-exposed groups were injected with Pseudomonas fluorescens (P. fluorescens) for 48h. At 24 and 48h post-injection with P. fluorescens (hpi), the lymphocyte numbers were strongly reduced at 0.3 and 1μg/L deltamethrin-exposed groups, whereas LYS and C3 levels were strongly reduced at 0.3 and 1μg/L deltamethrin-exposed groups (p<0.05). Obvious reduces in IgM levels were also detected at 0.3 and 1μg/L deltamethrin-exposed groups at 48hpi (p<0.05). The transcripts of almost all TLR signaling pathway-related genes were significantly down-regulated, whereas the levels of related microRNAs (miRNAs) were markedly increased at all deltamethrin-exposed groups at 24 and 48hpi. Moreover, the bacterial load in the liver and the mortality of fish were significantly increased at 1μg/L deltamethrin-exposed groups at 24 and 48hpi (p<0.05). Furthermore, obvious histological damage in the livers, intestines, and gills were observed at all deltamethrin-exposed fish at 48hpi. Overall, our results demonstrated that environmentally relevant concentration deltamethrin suppressed immunity and rendered the fish vulnerable to P. fluorescens infection, subsequently inducing mortality.