Effects of Different Exposure Time and Concentration of Zinc Oxide (ZnO) Nanoparticles on the Histopathological Changes of the Gill in Rainbow Trout (Oncorhynchus mykiss)

Extensive production of zinc oxide nanoparticle in science and industry can increases the risk of releasing this material into the environment in near future. Nanoparticles may cause a lot of damage at different levels after being released into aquatic ecosystems due to accumulation in the body and transfer to higher levels of food chains. To find effects of zinc oxide nanoparticles on the gill tissue in rainbow trout, 80 fish were randomly used with an average weight of 42.88 g in four plastic tanks (volume: 90 liters) and exposed to four different treatments with three replicates. The treatments were control (without ZnO), three treatments with concentrations of 0.025, 0.05 and 0.075 mg L‑1 zinc oxide nanoparticles (with an average size of 40-30 nm). Tissue samples were collected in four stages. The tissues were dewatered, placed in paraffin and cut using a microtome and finally stained with hematoxylin-eosin. To examine significant differences among treatments, a linear model based on rank data was used, with severe negative symptoms got the greater rank and data was analyzed using Rfit package in R. The observed changes indicated that zinc oxide nanoparticles may have significant effects on the gill tissue, therefore, the gill can be used as a biomarkers to assess impacts of environmental pollutants.