Spermatozoa represent one of the most sensitive stages of the life cycle in broadcast spawners, as they are directly released into the water column and immediately exposed to environmental contaminants. Among contaminants of emerging concern, fluoroquinolone antibiotics (FQs) such as enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) are increasingly detected in coastal waters, yet their direct effects on gametes remain largely unexplored. In this study, sperm from Mytilus galloprovincialis were exposed in vitro to environmentally relevant concentrations of ENR and CIP (5 and 500 ng/L). Sperm quality was assessed through motility, oxidative stress markers, mitochondrial activity, and DNA integrity. Fluoroquinolones can impair mussel sperm functionality through oxidative membrane damage, mitochondrial dysfunction, and potential genotoxic effects. These findings suggest that antibiotic pollution may compromise reproductive success in marine bivalves, with potential consequences for population dynamics and ecosystem resilience.
