Rainbow trout complement fixation used for titration of antibodies against several pathogens.

Since it is impossible to fix guinea pig complement (C) with Rainbow Trout (Salmo gairdneri) antibodies, whereas it is possible with Brown Trout (Salmo trutta) antibodies, a C fixation test has been designed which uses haemolysin and C from Rainbow Trout. Immunization of trout against lysed sheep red blood cells (SRBC) elicited production of haemolytic IgM. Normal trout serum (NTS) can be used as a source of C at a dilution at which its "natural" haemolytic activity (against various homeotherms RBC) has disappeared. Heating of trout C 30 min at 37 degrees C leads to a 75% loss of its activity, and this one is completely abolished at 40 degrees C. Fixation of 3 to 4 CH50 units has been achieved in a short test (2 h at 20 degrees C) for the following antigen-antibody systems: 2 bacterial antigens (Aeromonas salmonicida and Vibrio anguillarum); 2 viruses (Infectious Pancreatic Necrosis (IPN) virus and Egtved Virus). C fixation has a sensitivity comparable with agglutination in the case of A. salmonicida. For IPN Virus, sero-neutralization is 50 times more sensitive than C fixation. In the case of Egtved virus, the difference is not so great.