Parasites in aquatic ecosystems: to aquaculture and public health perspectives

Parasites are key components of aquatic ecosystems, contributing to biodiversity and ecological balance. In intensive aquaculture, however, their proliferation can compromise animal welfare and cause significant economic losses. High stocking densities, environmental stress, and reduced genetic diversity enhance transmission, while globalization and climate change favor the spread of pathogens and the emergence of novel host–parasite interactions. Sustainable control strategies are therefore essential to safeguard fish health, production efficiency, and environmental integrity. This thesis investigates the role and management of parasites in aquaculture, with a primary focus on Sparicotyle chrysophrii, a polyopisthocotylean monogenean infecting gilthead sea bream (Sparus aurata). Additional studies address parasitic risks in ornamental aquaculture and foodborne zoonoses in marine products. The first section evaluates essential oils (EOs) as natural alternatives to conventional chemotherapeutics. Sixteen phytogenic compounds were screened in vitro, and several showed strong parasiticidal activity against S. chrysophrii. Scanning electron microscopy revealed marked tegumental and muscular damage in treated parasites, confirming their direct effects. An in vivo trial then tested microencapsulated diets enriched with Origanum vulgare, Rosmarinus officinalis, and Cinnamomum zeylanicum oils in experimentally infected sea bream. Although parasite abundance was not significantly reduced, EO-supplemented diets improved survival and feed intake, suggesting beneficial physiological effects and complex host–parasite dynamics. The second section expands to other aquaculture contexts. The first record of Philometroides sanguineus in farmed goldfish (Carassius auratus) in Italy highlights biosecurity concerns linked to ornamental fish trade. Additionally, a survey of marketed squid documented zoonotic nematodes, including Anisakis simplex s.s., A. pegreffii, Hysterothylacium spp., and Lappetascaris spp., underscoring food safety implications. Overall, this thesis integrates parasitology, aquaculture, and food safety to promote sustainable aquatic health management, emphasizing phytogenic feed additives, preventive biosecurity, and continuous parasite monitoring.