Philasterides dicentrarchi (Ciliophora, Scuticociliatida): experimental infection and possible routes of entry in farmed turbot ( Scophthalmus maximus)

Philasterides dicentrarchi is a histophagous ciliate infecting turbot ( Scophthalmus maximus) in aquaculture, where it causes significant economic losses. However, the route of entry of these parasites in turbot is not known. In the present study, we attempted experimental infection by seven routes: nasal, oral, rectal, branchial/dermal (i.e. by immersion with or without previous abrasion of the gills and opercula), intraperitoneal, periorbital and intramuscular. Our results indicate that the natural route of infection is probably through lesions in the gills and/or skin, thus, assays which aim to mimic natural infection conditions should probably use immersion following branchial/dermal abrasion. However, in chemotherapeutic assays, where it is necessary to obtain severely infected fish in a fast and reliable manner, the most appropriate route for experimental infection is probably the intraperitoneal route.