Induction of immunosuppression to bacterial antigens in carp, Cyprinus carpio

Typical primary antibody responses were found after injecting carp maintained at 25°C with formalin‐killed (Fk) Vibrio anguillarum bacteria, but not in fish injected with the same antigen held at 12° C. There were no significant increases over the primary responses in fish receiving a second injection 60 days after the first injection. The differences in the results between fish groups receiving three V. anguillarum antigens at two dosages were found to be insignificant in most of the experiments. A comparison of the antibody titres of fish groups after challenge with Fk bacteria showed no difference from control fish receiving a single injection similar to the challenge dose or fish receiving a previous injection with the antigens emulsified in complete Freund's adjuvant (CFA) at 25° C. However, significant immunosuppression was found in fish that were given the primary injection intracardially at 25° C or 12° C, or with CFA emulsion at 12° C.