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Sulfide Treatment Alters Antioxidant Response and Related Genes Expressions in Rice Field Eel (Monopterus albus)

Sulfide is considered as an environmental factor and toxicant with a wide distribution in aquatic environments. At present, the toxic effects of sulfide stress on rice field eel (Monopterus albus) are poorly understood. To ascertain these effects, the juvenile rice field eels were exposed to sub-lethal concentrations of Na2S (0, 0.2154, 2.154, and 21.54 mg/L) for 7, 14, and 28 days. Antioxidant parameters such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and malondialdehyde (MDA) as well as the related gene (including sod, cat) expressions were measured. The expressions of metallothionein (mt) and heat shock protein 90 (hsp90), which are used as physiological stress indices, were also detected. The results showed that exposure to sulfide altered the antioxidant response and related gene expressions in rice field eel. The activities of SOD were inhibited and the MDA contents were increased after exposure to sulfide. The activities of CAT and GPx were increased at 7 days and decreased at 28 days after treatment with sulfide at the highest dose. The expressions of sod, cat, and hsp90 were upregulated at 7 days and downregulated at 14 and 28 days after exposure to high doses of sulfide. The expression of mt was significantly downregulated in all sulfide treated groups. The toxic effects caused by sulfide were in dose-dependent and time-dependent manners. In short, oxidative stress and physiological stress were caused in rice field eel after the exposure to sulfide.