Vaccination strategies in freshwater salmonid aquaculture.

The focus of this chapter is antibacterial vaccines. The main salmonid species in freshwater aquaculture is the rainbow trout. Other salmonid species are produced on a limited scale. The most important bacterial fish diseases in European freshwater aquaculture are the rainbow trout fry syndrome-RTFS-(Flavobacterium psychrophilum) and enteric redmouth disease-ERM-(Yersinia ruckeri) which are widespread and cause serious epizootics, while furunculosis (Aeromonas salmonicida) is endemic, only giving overt disease under extremely stressing conditions. In the hatchery, there is a need for vaccination against RTFS (not commercially available) and ERM; in the ponds it is urgent to vaccinate against ERM, while the importance of furunculosis vaccination is not clear. The fish for ongrowing in saltwater should be vaccinated against ERM, furunculosis and vibriosis. Commercial vaccines are available against these diseases, either as single component or combination vaccines for immersion and injection-and oral vaccines are under registration. Hitherto, there has not been much strategic research on vaccination in freshwater; however recent results suggest that with the regime of vaccines available (and soon available), fish should be vaccinated with an ERM immersion vaccine in the hatchery approximately four weeks before transfer to the ponds. To cover the growth period in fresh water an oral booster should be given two to three months later. There is a need for development and research in strategic use of an RTFS and a furunculosis vaccine in freshwater aquaculture.