Protective Immune Response in Rainbow Trout, Oncorhynchus mykiss, Vaccinated with β-haemolytic Streptococcal Bacterin

Abstract

Protective immunity against Streptococcal disease was investigated in rainbow trout, Oncorhynchus mykiss by immersion or intraperitoneal injection of a formalin-killed bacterin. Although no agglutinating antibodies were detected in the serum of fish vaccinated by the immersion method, antibodies were detected in the serum of fish vaccinated by intraperitoneal injection. Bactericidal activities of the serum of fish vaccinated by either the immersion or injection method did not increase. The phagocytic activities of the kidney increased in the vaccinated fish. When the vaccinated fish were challenged with the live pathogen, the number of streptococcal cells in the kidney, spleen, liver, and blood decreased gradually and, in most organs, streptococcal cells disappeared within 72 h of challenge.