Histopathological and biochemical responses to the oxidative stress induced by glyphosate-based herbicides in the rainbow trout (Oncorhynchus mykiss)

Abstract

This study aimed to determine the effects of glyphosate, a herbicide commonly used in weed control, on aquatic life. For this purpose, 30 one-year-old rainbow trout with an average weight of 150-165 g were obtained from a local trout production station in Mazmanlı (Hatay, Turkey) and transferred to our laboratory, where they were allowed to adapt to the new environment in polyethylene tanks approximately for 7 days. Three groups each containing 10 fish were formed: a control group with no treatment, the group treated with 1.25 mg/l glyphosate-based herbicide (GBH), and the group treated with 2.5 mg/l glyphosate-based herbicide. At the end of 14 days of treatment, blood samples were taken from the caudal vein of the fish under anaesthesia, and their sera were separated. Total oxidant/antioxidant levels and paraoxonase activity were analysed in the obtained serum samples. Also, for histopathological examination, gill tissues were removed and fixed in 10% buffered formalin. After the fixation and routine tissue processing (graded alcohols, methyl benzoate and benzol processing), the tissues taken were embedded in paraffin and 5 μm serial sections were taken by microtome from the blocks to slides pre-coated with chrome alum gelatine. Histopathological changes were examined at the light microscopic level by staining the sections with haematoxylin-eosin. According to the evaluation of the biochemical parameters obtained from the groups, antioxidant capacity and paraoxonase activity decreased and oxidant level increased in the group treated with 1.25 and 2.5 mg/l glyphosate-based herbicide as compared with the control group. In thehistopathological examination of the sections, it was observed that the primary and secondary lamellae had a normal structure in the gill sections obtained from the control group. Irregular secondary lamellae and epithelial hyperplasia were observed in the gill sections obtained from the group receiving 1.25 mg/l GBH. And in the gill sections obtained from the group receiving 2.5 mg/ l GBH, swelling in chloride cells, degeneration in secondary lamellae, and areas of necrosis were detected. In conclusion, results of the study suggests that glyphosate, which is widely used in agricultural activities and has a potential to leak into aquatic ecosystems, may cause oxidative stress due to reactive oxygen species formed in the rainbow trout, and may therefore has a toxic effect.