Acute Exposure to the Neonicotinoid Insecticide Imidacloprid of Zebrafish (Danio rerio) Gonads: A Histopathological Approach

Neonicotinoids are the new class of insecticides that are high target specificity to insects. Imidacloprid is a neonicotinoid that is the most widely used insecticide in the world. As a result of its widespread use in agriculture, imidacloprid interferes with the aquatic system and threatens the aquatic environment. In this study, an investigation of the histopathological effects of imidacloprid on zebrafish gonads was aimed. Zebrafish were exposed to 9.5 mg/L, 19 mg/L, and 38 mg/L of imidacloprid for 5 days, considering the 96 h LC50 value. After dissecting the gonadal tissues, routine histological techniques were applied, and the tissues were stained with Periodic Acid-Schiff (PAS), Toluidine Blue (TB), and Haematoxylin and Eosin (H&E). Sections were examined under a light microscope. While normal gonad histology was observed in the control group, histopathological alternations such as degeneration and union in the seminiferous tubules, hypertrophy in spermatogenic and Leydig cells, and interstitial fibrosis were detected in testicular tissue of the experimental groups. In the ovarian tissues of the experimental groups, structural deterioration in oocytes, autolysis, increase in the number of atretic oocytes, vacuolization in cortical alveoli, thickening and curling in the zona radiata, and opening in the perifollicular layers were detected.