Effects of Metamifop on Defense Systems in Monopterus albus

The effects of herbicides on non-target organisms in paddy fields have become a popular research topic. As a widely used herbicide, it is necessary to explore the potential toxicity of metamifop in non-target organisms, especially aquatic animals, in co-culture mode. In the present study, we evaluated the effects of metamifop (0, 0.2, 0.4, 0.6, and 0.8 mg/L) on the defense system (antioxidation, immunity, and apoptosis) in Monopterus albus. Reactive oxygen species (ROS) production, malondialdehyde (MDA) content, and protein carbonylation (PCO) increased significantly (p < 0.05) with the increasing metamifop concentration, resulting in oxidative damage. In the antioxidant system, superoxide dismutase (SOD) and catalase (CAT) activities increased significantly (p < 0.05) in the 0.2 mg/L treatment group compared with the control group, and decreased in 0.4, 0.6, and 0.8 mg/L treatment groups. Glutathione peroxidase (GPX) activity decreased significantly (p < 0.05) with the increasing metamifop concentration. In the immune system, white cell number (WCN) increased significantly (p < 0.05) in 0.2 mg/L treatment group, and then decreased with the increase in metamifop concentration. Compared with control group, acid phosphatase (ACP) activity not only increased significantly (p < 0.05) in 0.2 mg/L treatment group, but also decreased significantly (p < 0.05) compared with the increase in metamifop concentration. However, in all treatment groups, alkaline phosphatase (AKP) activity was significantly lower than that in the control group (p < 0.05). In the inflammatory response, TNF-α and IL-1β expression levels in the NF-κB signaling pathway decreased significantly (p < 0.05) with the increase in metamifop concentration, while IL-8 expression level in the same signaling pathway increased significantly (p < 0.05) in treatment groups. The expression levels of genes related to apoptosis showed that apoptosis was promoted after exposure to metamifop. The results of the present study show that metamifop induced oxidative damage via a high level of ROS production, and then inhibited or damaged the defense systems of M. albus.