PROTECTIVE IMMUNITY AGAINST ENTERIC SEPTICEMIA IN CHANNEL CATFISH, ICTALURUS-PUNCTATUS (RAFINESQUE), FOLLOWING CONTROLLED EXPOSURE TO EDWARDSIELLA-ICTALURI

Protective immunity against enteric septicaemia of catfish (ESC) follo wing immunization with Edwardsiella ictaluri bacterins and exposure to live E. ictaluri was investigated. Mean cumulative percentage surviva l was significantly higher (P less than or equal to 0.05) in controlle d live vaccinates (100%) than in immersion and oral bacterin vaccinate s (68.3% and 50.0%, respectively). Bactericidal activity against E. ic taluri by peritoneal macrophages from controlled live vaccinates (85.9 %) was significantly greater (P less than or equal to 0.05) than bacte ricidal activity of macrophages from immersion bacterin vaccinates (71 .4%) or non-vaccinates (68.1%). No significant (P > 0.05) difference w as found in the bactericidal activity of macrophages from oral bacteri n vaccinates and macrophages from controlled live vaccinates. The E. i ctaluri-specific antibody response of controlled li ie (0.08 OD) and i mmersion bacterin vaccinates (0.11 OD) was significantly higher (P les s than or equal to 0.05) than that of oral bacterin vaccinates and non -vaccinates (0.01 OD) 15 days post-vaccination. A significantly higher antibody response was seen in controlled live vaccinates (0.17 OD), w hen compared re other vaccinates or non-vaccinates 33 days after vacci nation. Neither immersion nor oral bacterins protected the vaccinates against ESC. Controlled live E. ictaluri immunization of channel catfi sh resulted in production of specific antibodies, increased macrophage bactericidal activity and protection against ESC.