Histopathological changes in the gills of Astyanax lacustris specimens exposed to a reactive textile dye, before and after treatment with the constructed wetland system

Abstract Reactive dyes commonly used in the textile industry have been found to pose potential harm to aquatic organisms. In light of the lack of comprehensive studies on the effects of reactive dyes, our study aimed to assess the impact of Novacron® Bold Deep Navy reactive dye on the gills of Astyanax lacustris. Specifically, we sought to determine the toxicity of the dye before and after treatment using a vertical flow constructed wetland (VFCW) system. During the experiment, A. lacustris specimens were exposed to sublethal concentrations (10, 20, 30, and 40 mg L-1) of Novacron® Bold Deep Navy dye and to dye treated by the VFCW for 96 hours. Our findings indicated that the dye led to significant gill damage, including secondary lamellar fusion, hyperplasia, hypertrophy of lamellar epithelial cells, telangiectasia, and aneurysm, compared to the control group (p < 0.05) at all concentrations. Scanning Electron Microscopy (SEM) images revealed the disappearance of microdigitations as the dye concentration increased. The VFCW system demonstrated efficient bioremediation of the dye, as evidenced by reduced gill damage and favorable physical-chemical analyses. These results emphasize the potential risk of dye to aquatic organisms, while also showcasing the effectiveness of the VFCW system in removing the dye.