Eugenol-parasite interactions in ten spotted live-bearer fish Cnesterodon decemmaculatus: Seasonal and host-related effects

The widespread use of synthetic antibiotics and chemicals in aquaculture to control parasitic infections poses environmental and health risks, including antibiotic resistance and harm to aquatic organisms. Consequently, there is growing interest in natural, sustainable alternatives for parasite control in both wild fish and aquaculture. This study examines the efficacy of eugenol and its effects on parasitic infections and infestations in the ten spotted live-bearer fish Cnesterodon decemmaculatus, found in South American freshwater ecosystems. The study focuses on ectoparasites such as Trichodina spp., as well as endoparasites including Echinostomatidae, and Ascocotyle sp., which affect the skin and gills, Ascocotyle sp. metacercariae in the heart, Pygidiopsis sp. metacercariae infecting the liver and coelomic cavity, and Saccocoelioides kirchnerii infecting the intestine. Seasonal and host sex-related differences in parasitic mean abundance (MA) and prevalence were also considered. Seasonal variations were observed in Echinostomatidae, Trichodina spp., and Ascocotyle sp. Eugenol significantly reduced the MA of Trichodina spp. (P = 0.001). Larger fish exhibited higher parasitic MA, with significant correlations observed for total length (TL) (P = 0.03) and standard length (SL) (P = 0.02). This study contributes to the understanding of natural antiparasitic agents in aquaculture and their potential for sustainable parasite management.