SPREADING OF THE SWIMBLADDER PARASITE CYSTIDICOLA FARIONIS (NEMATODA: CYSTIDICOLIDAE) IN WILD AND FARMED SALMONIDS IN ITALY

Cystidicola farionis is a nematode frequently reported in swimbladder of several species of wild salmonids from USA and Europe, and recently described in Italy. The life cycle is heteroxenous and involves as intermediate hosts several species of gammarid crustaceans widespread in the freshwater aquatic environment. After the previous report in salmonids (Salmo trutta fario and Oncorhynchus mykiss) from the wild in the northern part of Adige River (Bolzano province), the infestation seems to progressively widen its geographical area. During an ongoing parasitological survey on salmonids, high prevalence (P%) and mean intensity (MI) values of infestation have been recorded in wild salmonids (P% range 28.6-70%; MI range: 4.5-100) and in farmed rainbow trouts (P% range: 37.5-100%; MI range: 4.5-12.5) in northern Italy, expanding to different regions (Veneto and Friuli Venezia-Giulia). The pathogenicity and the impact of C. farionis on health of affected fish is still debated among the scientific community. Anyway in this study some gross lesions in heavily affected fish have been observed, such as a catarrhal-hemorrhagic inflammation of highly infected swimbladder, more severe in juvenile wild brown trout (S. trutta fario). Furthermore, although C. farionis has been generally detected at low intensity in farmed trout, it could affect productivity and quality of fish products and so has to be considered a potential health risk for national aquaculture. Although the authors in past surveys already alerted on the possible C. farionis switching from wild to farmed salmonids and vice versa, no preventive strategies to avoid the expanding of C. farionis geographic range have been adopted. Further studies are urgent to map the actual distribution of cystidicolosis in Italian salmonid populations and to apply appropriate containment measures useful to avoid its further spread.