Marine phycotoxins repurposed as bioresource: their antiviral potentials and molecular mechanisms in aquatic organism.

UNLABELLED: Marine phycotoxins produced by microalgae have traditionally been regarded as water pollutants or hazardous substances. Most studies have focused on their toxicity, with limited exploration of their therapeutic potential. In this study, we demonstrated that domoic acid (DA) exerts antiviral roles against largemouth bass ranavirus (LMBV). Mechanistic analyses revealed that DA disrupts the extracellular structure of LMBV and inhibits intracellular viral assembly. This may be attributed to the ATP depletion caused by the suppression of mitochondrial oxidative phosphorylation. In vivo, DA treatment reduced fish mortality by 12.5% and significantly alleviated pathological lesions in splenic and telencephalic tissues, thereby further confirming its protective effect. Additionally, transcriptomic analysis of liver tissue showed that DA enhanced digestive enzyme activity and activated the complement immune response in LMBV-infected fish. This study uncovers previously unappreciated antiviral activity of marine phycotoxin-DA and elucidates its underlying mechanisms preliminary, laying a foundation for developing marine phycotoxins as antiviral lead compounds. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1007/s42995-026-00412-2.