BROOK CHARR, SALVELINUS-FONTINALIS (MITCHILL), AND CRYPTOBIOSIS - A POTENTIAL SALMONID RESERVOIR HOST FOR CRYPTOBIA-SALMOSITICA KATZ, 1951

Laboratory-raised Cryptobia-susceptible brook charr, Salvelinus fontin alis (Mitchill), and rainbow trout, Oncorhynchus mykiss (Walbaum), wer e vaccinated intraperitoneally with a live Cryptobia salmositica vacci ne (250000 parasites per fish), and 4 weeks later were challenged with the pathogen (250000 parasites per fish). Unvaccinated and infected b rook charr had high parasitaemias but no clinical signs of disease, wh ile unvaccinated and infected rainbow trout had anaemia and general oe dema. Vaccinated and challenged fish had very low parasitaemias compar ed to unvaccinated and infected brook charr and rainbow trout. Complem ent fixing antibodies were detected in vaccinated and challenged fish 2 weeks after challenge. Unvaccinated and infected brook charr had con sistently higher titres of complement fixing antibody than unvaccinate d and infected rainbow trout. Parasitaemias were lower in all fish in which titres of complement fixing antibody were high. In a second expe riment, brook charr inoculated intraperitoneally or intramuscularly wi th 100000 C. salmositica per fish had high parasitaemias but no anaemi a or other clinical signs. The results show that susceptible brook cha rr do not suffer from cryptobiosis and may serve as reservoir hosts fo r C. salmositica in areas where the disease is prevalent. Vaccination to reduce the parasitaemia when fish become infected may be a control strategy in these areas.