Immunization of rainbow trout, Salmo gairdneri Richardson, against bacterial kidney disease: preliminary efficacy evaluation

Abstract. A bacterin for immunization against bacterial kidney disease of salmonid fishes caused by Renibacterium salmoninarum is described. Cultures were grown in Evelyn's KDM2 medium containing 10% calf serum in a fermenter under the following conditions: pH 7.2, 15°C, 800ml/min air, 200 rev/min agitation and 5–15 days of incubation. Possible substitutes for calf serum were 10% horse serum 0.15% starch and leptospira medium. The bacterins were inactivated with 0.3% formalin and no adjuvants were used. Other tests evaluated pH-lysed bacterin, 50% concentrated bacterin and 50% concentrated pH-lysed bacterin. Juvenile rainbow trout, salmo gairdneri Richardson, were vaccinated either by intraperiotoneal (i.p.) injection, 2 min immersion or 2-step hyperosmotic infiltration. Fish were held from four to six weeks at 11°C, then challenged by i.p. injection with the homologous virulent bacterium. Fish died from days 19 to 40 after challenge. The best preparation was pH-lysed bacterin given by a single i.p. injection; hyperosmotic and immersion vaccination were not effective. Typically when 80% or more of unvaccinated controls were infected as detected by Gram stain, 10% or less of the vaccinated fish were infected.