Goussia carpelli (Protozoa : Coccidia) infection in stressed and immunosuppressed common carp Cyprinus carpio

Goussia carpelli causes enteritic coccidiosis in juvenile carp. In nature i t affects carp fry (1 to 2 mo old) and fish (3 to 4 mo old) which are subje cted to environmental stress. Carp treated with corticosteroids or subjecte d to temperature stress in the laboratory produced higher numbers of oocyst s during the primary infection. Resistance to reinfection via the fecal con tamination route, however, was not reduced by the application of hydrocorti sone, dexamethasone, or X-ray irradiation given both prior to and concurren tly with reinfection. The administration of hydrocortisole or irradiation d id not induce a relapse of a previous infection. Carp which had been immuno suppressed by hydrocortisole injection during a primary infection were also refractory to a secondary infection via fecal contamination. The results o f these experiments suggest that the mechanisms which are responsible for t he resistance of carp to secondary infections with Goussia carpelli were no t affected by hydrocortisole, dexamethasone or X-ray treatment.