Fluorene-induced antioxidant disruption, neurophysiological impairment, and DNA damage in freshwater snail (Bellamya bengalensis) and fish (Anabas testudineus): Evidence from in vivo and in silico studies.

Fluorene (FL), a low-molecular-weight polycyclic aromatic hydrocarbon (PAH), is increasingly detected in freshwater environments, yet its mechanistic toxicity remains poorly characterized. This study evaluated FL-induced toxicity in Bellamya bengalensis (BB) and Anabas testudineus (AT) under acute (96hrs) and chronic exposures (28 and 45 days respectively). Acute assays revealed concentration-dependent mortality, with 96-h LC50 values of 3.074 mg/L for BB and 1.991 mg/L for AT, indicating higher fish sensitivity. Behavioral impairments-reduced crawling and mucus secretion in BB, and erratic swimming, equilibrium loss, and opercular changes in AT-signaled early neurophysiological disruption. Chronic exposure (10 % and 20 % LC50) caused significant oxidative stress, tissue damage, and DNA fragmentation, corroborated by elevated tail length and tail moment in the comet assay. Molecular docking provided mechanistic support, revealing strong fluorene affinity for catalase and DNA polymerase in BB (-6.8 and -6.1 kcal/mol) versus DNA topoisomerase in AT (-6.2 kcal/mol). These interactions, dominated by π-π stacking and hydrophobic contacts, suggest catalytic inhibition and structural destabilization of antioxidant and genomic enzymes. Consequently, oxidative stress emerged as the primary toxicity pathway in BB, while replication stress and genotoxicity dominated in AT. Histopathological lesions-epithelial atrophy in BB and hepatocellular hypertrophy in AT-further reflected divergent metabolic responses. Collectively, the cross-species evidence highlights that even a structurally simple PAH such as fluorene exerts complex, multi-level effects through conserved molecular targets. These findings underscore species-specific vulnerabilities and demonstrate the ecological and regulatory importance of incorporating in silico-in vivo integration in aquatic PAH risk assessment.