Morphological and immunohistochemical modifications in Zebrafish (Danio rerio) gills after short-term exposure to the fungicide tebuconazole

In agroecosystems, a variety of pesticides may enter aquatic habitats exerting a number of toxic effects on living organisms. Due to their wide use and the repeated application, fungicides can be found at a much greater concentration than other agrochemicals in all environmental compartments. One of these fungicides, tebuconazole (TBZ), has been recognized as an endocrine-disrupting chemical, and the available literature focuses mainly on this mechanism of action. In the present study by subjecting the zebrafish model to an environmentally realistic concentration of TBZ, we clearly demonstrate that this fungicide has the potential to induce severe morphological and ultrastructural alterations in gills. The main morphological effects recorded in this study were as follows: the proliferation of the main epithelium, ectopia of chloride cells, lamellar shortening, necrosis, and apoptosis. TBZ exposure also resulted in the overtime decrease in the expression of both Na+/K+-ATPase and aquaporin 3 and in the induction of oxidative stress enzyme (superoxide dismutase-1) as revealed by immunohistochemical analysis. Our results clearly indicate that respiratory and osmoregulatory disorders represent an important mechanism of TBZ toxicity on Danio rerio gills. This is the first evidence of sublethal effects exerted by TBZ on fish gills and highlights the harmful properties of this fungicide, even at very low concentration.