Ethical considerations in lethal sampling of aquatic vertebrate hosts in parasitological studies

Studying parasites in aquatic vertebrate hosts is vital for understanding parasite diversity, life cycles, host-parasite associations and parasite-environment interactions. However, such research often requires euthanizing hosts, raising ethical concerns amid increasingly stringent animal welfare standards. This opinion article examines whether and when killing aquatic vertebrate hosts for parasitological studies is ethically justifiable. We outline current ethical regulations and review processes, then consider legitimate reasons for host sacrifice - such as accurate parasite identification, biodiversity assessment, and ecosystem health monitoring. Emphasising the multiple Rs framework in parasitological research we propose practical strategies to minimise harm, including non-lethal diagnostics and improved methodologies. Our goal is to foster critical reflection and promote more ethical, innovative approaches within aquatic parasitology.