Search

After the discovery of I. hoferi disease in Norwegian spring spawning herring in summer 1991, a program for systematic surveillance of the disease in the herring in Norwegian waters was developed. The programme, which aims primarily at monitoring the prevalence of the disease, is described. Macroscopic lesions in the heart emerged as the standard diagnostic criterium. The results so far indicate that the situation for Norwegian spring spawning herring is not alarming, altohough it still deserves attention. For the North Sea herring, the situation is less clear. The diseased herring seem to be less prone to follow normal scooling behavior, which causes sampling problems that must be taken into account when interpreting prevalence results.

Wild Atlantic salmon (Salmo salar) were captured in four rivers in western Norway in 1989 and 1990. These were used as broodstock fish in a sea ranching project. In 1989 virological and bacteriological examinations of the fish were negative for Infectious Pancreatic Necrosis Virus, Renibacterium salmoniarum, Aeromonas salmonicida var. salmonicida and Yersinia ruckeri. In 1990 three fish were positive for IPNV and one fish was positive for Aeromonas salmonicida var. salmonicida. The results supply the mapping of the introduction of furunculosis at the Norwegian west coast in 1989-90, indicate a low prevalence of Infectious Pancreatic Necrosis Virus in the wild salmon stocks and states that the broodstock fish used in the sea ranching project in 1989 and 1990 were tested in accordance with the demands for a satisfactory health control.

Arctic char of six different strains have been vaccinated against vibriosis and a relative protection (RPP) of 98% was demonstrated by waterborne challenge. This species is highly susceptible to vibriosis and the gross pathology is similar to vibriosis in rainbow trout. Sex maturation and genetics may have some impact on disease resistance.

Atlantic salmon smolts (Salmo salar) were vaccinated with a bacterin made from formalin-killed Vibrio salmonicida. In laboratory trials, fish vaccinated once showed little or no protection after challenge. Fish vaccinated twice appeared to be protected, the degree of protection depending on the administration route of the vaccine.