Acetylcholinesterase activity, histopathological changes, lipid peroxidation and stress-related genes expression in Nile tilapia (Oreochromis niloticus) exposed to waterborne methidathion

The safety of aquatic system has been threatened due to extensive and inappropriate application of organophosphorus pesticide methidathion (MD). Hence, a 12-day stress trial was carried out to explore the impacts of waterborne MD on acetylcholinesterase (AChE) activity, histopathology, antioxidant status and stress-related genes expression in Nile tilapia (Oreochromis niloticus). Fish (initial mean weight 60 ± 2 g) were placed in 18 tanks (volume 460 L, 30 fish/tank), with triplicate treatment groups being exposed to diverse concentrations of MD (0, 0.8, 1.67, 5.34, 7.49 and 15.83 µg/L). The results showed that AChE activities in serum and liver were inhibited by MD. After the 12-day stress trial, malonaldehyde (MDA) content in serum and liver was higher than that of 0 µg/L group when MD concentration exceeded 0.8 and 5.34 µg/L, respectively. Catalase (CAT) and total superoxide dismutase (T-SOD) activity in serum and liver revealed irregular variations. In addition, MD (＞0.8 µg/L) caused lesions in gills and liver tissues. MD also down-regulated expression of cytochrome P450 1B1, heat shock protein 70 and cytochrome c oxidase subunit 7B, which contradicted the trend of phospholipase A2 and cytochrome P450 1 A (except in the 15.83 µg/L group). In a word, waterborne MD suppressed AChE activities, induced oxidative stress and harmed the liver and gills. Additionally, it may negatively influence resistance to stress, oxidative phosphorylation, detoxification and anti-inflammatory response in Nile tilapia.