A historical review of fish vaccinology.

The first report on fish vaccination to appear in a widely read international scientific journal was that by Duff [5] dealing with his results obtained with anti-furunculosis vaccines. Duff's report did not result in an immediate landslide of fish vaccination trials in other laboratories because, in the years following the second world war, the preoccupation was with disease control using the newly discovered antibiotics. In fish culture, the ensuing 30 to 40 years might accurately have been termed the "era of chemotherapy" because large numbers of antibiotics, sulpha drugs, and even mercury-based antimicrobial agents were routinely used. It was only in the mid to late 1970s, with an increased interest in fish farming, particularly marine fish farming, that attention was once again turned to the possibility of vaccination as a means of preventing/ controlling fish diseases and to the development of commercially available vaccines. The reasons for this turn of events were varied: the high cost of using chemotherapy, the short-term nature of the protection obtained with antibiotics, the increasing appearance of antibiotic resistant fish pathogens, and, to some extent, concerns about the environmental impacts of antibiotic use. This paper briefly outlines the success that has attended efforts to develop vaccines against some of the more important bacterial diseases of cultured fish and the progress made in developing vaccines against important viral fish pathogens. In the process, an attempt will be made to show how fish vaccine development has benefited from an improved knowledge of the fish's immune system and from a better understanding of the virulence factors possessed by particular fish pathogens.