VACCINATION OF RAINIBOW TROUT, ONCORHYNCHUS-MYKISS (WALBAUM), AGAINSTCRYPTOBIOSIS - EFFICACY OF THE VACCINE IN FRESH AND SEA-WATER

Adult rainbow trout, Oncorhynchus mykiss (Walbaum), maintained in eith er fresh or sea water were vaccinated with a live Cryptobia salmositic a vaccine. All vaccinated fish were protected 4 weeks later against th e cryptobiosis, while unvaccinated rainbow trout developed the disease (e.g. high parasitaemia and severe anaemia) after challenge with viru lent C. salmositica. There was also no disease in vaccinated fish when they were transferred from fresh to sea water immediately after vacci nation. Complement fixing antibodies (CFAbs) were detected in vaccinat ed fish and the CFAbs lysed parasites under in vitro conditions. The a ntibody titres increased rapidly at one week postchallenge in vaccinat ed fish in fresh water and vaccinated fish transferred from fresh wate r to sea water after vaccination. However, the production of CFAbs was delayed by one week in vaccinated fish in sea water and the antibody titre was significantly lower than that in fish maintained in fresh wa ter.