Structural abnormalities in erythrocytes and a potential denucleation process induced by metformin, compromising cell viability in specimens of Astyanax lacustris (Pisces, Characidae).

Hematological studies in fish are sensitive indicators of physiological and pathological changes caused by aquatic pollution, including pharmaceutical contaminants. Among these pollutants, metformin is one of the most prevalent and has been associated with adverse effects on aquatic organisms. However, its impact on fish erythrocyte morphology remains poorly understood. This study evaluated the cyto- and genotoxic effects of metformin on erythrocytes of Astyanax lacustris through morphological analyses, membrane integrity assessment by flow cytometry, and DNA damage evaluation using comet assay. Fish were exposed to metformin concentrations of 50, 100, and 10,000 µg/L for 90 days. Exposure induced significant erythrocyte alterations, particularly at higher metformin concentrations, including membrane invaginations and ruptures, cytoplasmic vacuolization, nuclear abnormalities, DNA damage, peripheral nuclei, and formation of erythroplastids, suggesting denucleation process. Flow cytometry also revealed an increased proportion of non-viable cells. These findings suggest that metformin may significantly impair erythrocyte physiology and viability, potentially compromising the health of exposed fish.