Seasonal change in serum agglutination titer against Renibacterium salmoninarum in farmed masu salmon Oncorhynchus masou
2006
Hatakeyama, M.(Hokkaido. Fish Hatchery, Eniwa (Japan)) | ; Miura, K.
Chronic bacterial kidney disease (BKD) in masu salmon, Oncorhynchus masou was investigated at a fish farm. In previous cases at the farm, BKD broke out concentrating in the spring-to-early-summer season. To clarify the factors of the seasonal limitation of an outbreak, the BKD infection rate of the fish was determined by isolating Renibacterium salmoninarum at certain intervals. In addition, the agglutination titer against R. salmoninarum and total immunoglobulin M (IgM) levels of the fish serum were researched as indications of host reactions against the bacteria. A seasonal change in the agglutination titer against R. salmoninarum was found. The characteristics of the seasonal change in the titer were a moderate increase from summer at age 0sup(+) until winter at 1sup(+), an acute decrease in spring at lsup(+), a moderate recovery from summer at 1sup(+) until winter at 2sup(+), an acute decrease in spring at 2sup(+) and a moderate decrease until spawning. A seasonal change in the agglutination titer was also found in the fish group that was negative on the bacterial isolation. The seasonal change in the agglutination titer did not completely accord with the seasonal changes in total IgM levels or water temperature. From the characteristics of the seasonal change in the agglutination titer and the past timing of outbreaks on the farm, the occurrence of BKD was considered to be closely correlated with a decrease in the agglutination titer against R. salmoninarum.
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