Studies on Bacterial Kidney Disease in Atlantic Salmon (Salmon salar) in Canada

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The widespread nature of Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD) among salmonid fish, was demonstrated in trout and salmon samples taken over the past 20 years from freshwater streams and salt water sites located on Cape Breton Island, Nova Scotia, Canada. Although ubiquitous in this area, major mortalities have been reported from only a few isolated locations. However, heavy losses do occur when infected fish are acclimated to sea water prior to their salt water phase of life. The diagnosis of bacterial kidney disease, which once depended on the Gram stain of a kidney smear, now utilizes more sensitive, serological confirmation techniques such as the fluorescent antibody technique or precipitin test.
In Atlantic salmon smolts, this disease exists in many internal organs but bacterial numbers concentrate in the kidney and proliferate as the temperature surpasses 4°C in the Spring. In advanced infections, lesions or bacterial pustules form on several organs but most often on the kidney.
We have investigated vaccination and nutrition as possible prophylactic methods to minimize BKD infection occurrence and severity. In vaccination trials, post yearling Atlantic salmon parr administered a 0.1 ml intraperitoneal injection of formalin killed BKD cells emulsified in Freund's complete adjuvant showed an elevated agglutinating antibody response and almost complete absence of BKD lesion formation in the kidneys. In the nutritional studies, a reduction in the incidence of BKD infections with lesions was observed in the July sample among fish fed diets with a high concentration of trace elements or a low calcium content. This therapeutic effect was attributed to the increased availability of trace elements for metabolic purposes.