First Report of Philometroides sanguineus (Nematoda: Philometridae) in Farmed Goldfish (Carassius auratus) in Italy.

The ornamental fish trade has facilitated the global dissemination of parasites, posing significant biosecurity risks. This study documents the first detection of the nematode Philometroides sanguineus in farmed goldfish (Carassius auratus) in Emilia-Romagna, Italy. Specimens of gravid females, found in the caudal fins, and males, collected from the swim bladder, were identified through morphological, molecular and scanning electron microscope (SEM) analyses. This report underscores the risk of nonnative pathogen introduction via ornamental fish translocation, and the possibility of their spreading through the aquatic environment. In fact, the role of intermediate hosts, such as copepods, in parasite dissemination emphasises the need for stricter controls in systems reliant on surface water. Although P. sanguineus infection did not cause significant mortality in adult fish, its presence diminishes the ornamental value of infected specimens and raises concerns about the parasite's spread to native ecosystems. This case highlights the need to improve the biosecurity measures and comprehensive risk assessments to mitigate the introduction and propagation of alien parasites in aquaculture systems. Further research is necessary to evaluate the parasite's epidemiology, distribution and potential pathogenicity under different environmental and farming conditions.