Environmental change is contributing to change the pattern of diseases in aquatic settings. In this study we have analyzed the disease outbreaks that occurred in North Spanish Salmonid hatcheries during the last two decades. Six pathogens were considered: Aeromonas hydrophila, Aeromonas salmonicida, Flavobacterium psychrophilum, Lactococcus garvieae, infectious pancreatic necrosis virus and Yersinia ruckeri. Vaccines against Lactococcus and Yersinia are currently applied in the region. A shift in the dominant pathogen from Y. ruckeri to F. psychrophilum occurred after the year 2000, coincident with application of vaccines and climate warming in the region. Positive association of vaccines against some pathogens and prevalence of other pathogens was found, as well as a significant change in the temperature range at which outbreaks occurred. Both environmental perturbations and opportunistic development of pathogens when others are controlled by vaccines contribute to explain the stability of disease outbreaks in the region despite the introduction of vaccines.
