<p>The current study investigated the toxicological effects of 4-bromodiphenyl ether (BDE-3) through biochemical, genotoxic, histopathological, ultrastructural (SEM) and ATR-FTIR analysis in the gill and liver of adult zebrafish. After LC₅₀ determination, zebrafish were exposed to 0.48&#xa0;mg/L and 0.97&#xa0;mg/L of BDE-3 for 96&#xa0;h. A significant increase in MDA content and GST activity was observed in the gills and liver of the 96&#xa0;h exposure groups. The SOD activity was found to be significantly depleted in the gill and liver of BDE-3 exposed zebrafish. The AChE activity was found to be significantly decreased in the gills, whereas in the liver, AChE activity was significantly elevated. The DNA damage measured by tail length (TL) and tail intensity (TI) was found to be significantly increased in both tissues. The histopathological study revealed various anomalies, including elongated secondary lamellae, curled and fused secondary lamellae, distorted secondary lamellae and epithelial lifting in the gills and sinusoid dilation and congestion, cellular vacuolization, necrosis and erythrocyte infiltration in the liver. The ultrastructural (SEM) analysis also reaffirmed the different types of alterations in gill and liver tissue. The ATR-FTIR revealed the structural alterations in different biomolecules in the gills and liver of zebrafish after BDE-3 exposure. The results of the present study demonstrated increased lipid peroxidation, altered antioxidant enzymatic activities, elevated DNA damage and pronounced histopathological, ultrastructural and biomolecular alterations in the gill and liver tissues of zebrafish exposed to sub-lethal concentrations of BDE-3, indicating its significant toxic potential.</p>