Effect of immersion booster vaccination with Yersinia ruckeri extracellular products (ECP) on rainbow trout Oncorhynchus mykiss

Extracellular products (ECP) of bacteria is a factor responsible for a number of biological effects including immunostimulatory activities in different animals including fish. In this study, the effect of extracellular products (ECP) of Yersinia ruckeri on protective immunity in rainbow trout was investigated. To obtain an effective vaccine against the Yersiniosis, ECP preparation was obtained from the Y. ruckeri and the immersion twice into the rainbow trout was carried out.After 60 days vaccinated fish with first and second immunization by ECP were challenged via intraperitoneal injection with 9.8 x 106 cell/ml of Y. ruckeri. The protection against challenge was obtained by the vaccination (74.0– 81.4% relative percentage survival (RPS)), but the fish from the control group had an 67.5% of mortality rate. The results indicated that the vaccinated fish showed higher non-specific immune activity and protective effect than did the unvaccinated fish. The results suggest that the administration of ECP at rainbow trout is safe and elicits protection upon pathogen challenge.