Pathological and histometric analysis of the gills of female Hyphessobrycon eques (Teleostei:Characidae) exposed to different concentrations of the insecticide Dimilin®

•First record of sublethal exposure of Hyphessobrycon eques to Dimilin® insecticide.•Fish were exposed to concentrations of 0.01, 0.1 and 1 mg L−1 for 96 h and 17 days.•Low concentrations of Dimilin® caused mild to moderate changes in fish gills.•Histometric changes of vessels and lamellae can negatively influence gas exchange.•Increased number of chloride and mucous cells indicate the initiation of adaptation.

Female individuals of Hyphessobrycon eques were exposed to Diflubenzuron (Dimilin®) in order to determine whether exposure to sublethal levels of this insecticide causes changes in gill morphology. Fish were exposed to 0.01, 0.1 and 1.0 mg L−1 for 96 h and 17 days and then submitted to pathological and histometric evaluation. Pathological lesions, such as hyperplasia, lamellar fusion, vascular congestion, secondary lamellar disarray, vasodilatation, hemorrhage and increased lamellar epithelium, were significantly more common in the gills of fish exposed to Dimilin® than the control. Histometric analysis documented significant changes in blood vessel diameter, primary lamellae width and secondary lamellae length, and the appearance of hemorrhage foci in all concentrations tested. Even at low Dimilin® concentrations, the histopathological alteration index was mild to moderate, thereby indicating that the function of this tissue was compromised. These findings indicate that indiscriminate use of Dimilin® can adversely affect the structural integrity of the gills of H. eques, which can cause numerous problems for fish farming systems.

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