In Vivo Screening for a Promising Antiparasitic Agent Against Neobenedenia melleni in Epinephelus fuscoguttatus♀ × E. lanceolatus♂ and Identification of Its Potential Target
Monogenean ectoparasites, particularly Neobenedenia species, cause severe economic losses in mariculture. Here, ectoparasites isolated from cultured hybrid groupers (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) were confirmed as Neobenedenia melleni based on ITS1 phylogeny. In vivo screening of six structurally diverse compounds identified compound D (CAS No. 206111-37-7), a 5,6-dihydropyridine derivative, as the most effective antiparasitic agent, achieving 76.54% efficacy at 0.5 mg/L in a 90 min bath treatment. Dose-response assays demonstrated that 0.7 mg/L compound D achieved 95.23% antiparasitic efficacy without causing evident tissue damage or cytotoxicity to GF-1 cells. Ultrastructural observation by scanning electron microscopy revealed marked tegumental alterations, including deep fissures and extensive surface folding, in treated parasites. Molecular docking against ten candidate proteins identified β-tubulin as the most favorable docking target, with a binding energy of −6.53 kcal/mol and three hydrogen-bond interactions, suggesting that β-tubulin may be involved in the antiparasitic activity of compound D. Overall, these findings highlight compound D as a promising lead candidate for short-bath therapy against N. melleni and suggest that cytoskeletal disruption through β-tubulin interaction represents a plausible mechanism of action.