Effect of ammonia on the survival and the immune response of rainbow trout (Oncorhynchus mykiss, Walbaum) vaccinated againstStreptococcus iniae

The effect of sublethal concentrations of ammonia on the survival and the antibody response of rainbow trout (Oncorhynchus mykissWalbaum), vaccinated against and challenged withStreptococcus iniae, was examined in this study. The relative percent survival (RPS) of vaccinated fish exposed for 1 month to low (NH3μg l−13μg l−13μg l−1S. iniaestrain was examined during 1 month following challenge. There was no difference in the RPS of trout maintained at low and medium ammonia levels, but the RPS of fish exposed to the high ammonia level was significantly lower. Long term exposure of vaccinated trout to medium ammonia concentrations reduced the RPS as compared with control vaccinated fish. There was no correlation between antibody titres and exposure to ammonia and protection. Based on passive transfer of immunity by antibodies, it was concluded that the decrease of protection againstS. iniaein ammonia-exposed trout could be attributed to suppression of the cellular or the non-specific defence mechanisms or to the effect of ammonia on other physiological systems (vascular, respiratory, etc.).