Matrix changes due to the toxic effects of metronidazole in intestinal tissue of fish (Onchorhynchus mykiss).

Metranidazole (MTZ) is an antibiotic used for parasitic infections in a number of species. Accumulation of this drug in the environment and its interaction with fish of economic value makes this drug particularly important. In the present study, we examined the histopathological effects of MTZ on the intestinal tissue of Oncorhynchus mykiss. The fish in aquarium were exposed to MTZ at doses of 5, 10, 20 mg/L for 2, 4 and 8 days. At the end of the experiments, macroscopic pathology or death were not observed at these doses. Histochemical staining with Haematoxylene-Eosin, Periodic Acid Schiff and Gomori Trichrome showed, depending on increased dose and prolonged duration, areas of necrosis, edema, inflammation, small tears at the tips of the villi and excretion with heterogenic distribution of the Goblet cells. Moreover, changes in the connective tissue of the intestines due to toxicity of MTZ and decreases in immunostaining of matrix proteins such as laminin and collagen IV, especially in the epithelium were observed. Findings of the present study would be useful to demonstrate the adverse effects of MTZ use, emphasizing the importance of the effect on fish which could be very important public health.