Morbidity of Tagged Wild Adult Fall Chum Salmon Captured by Fish Wheel in the Yukon River, Alaska

摘要

A mark-recapture study using fish wheels and spaghetti tags was conducted annually on migrating Yukon River chum salmon since 1996. A substantial decrease in the relative abundance of tagged fish was observed with increased distance upstream, potentially indicating excessive mortality of tagged fish. To evaluate causes of mortality and morbidity and describe histologic changes during migration, chum salmon were sampled and examined by full necropsies that included external lesions, weight, length, hematology, bacteriology, ELISA for bacterial kidney disease antigen, and semiquantitative histopathology. To assess body condition, Fultons condition factor, hepatosomatic and gonadosomatic, indices, were determined. None of these analyses indicated a definitive cause for mortality or morbidity specific to the tagged fish. Local damage at the tag site, higher neutrophil numbers, and lower total protein in tagged fish suggested further study into the possibility of infection as a cause of mortality associated with tagging. A single untagged fish had a systemic infection of Aeromonas salmonicida. These bacteriology results indicated that septicemia from tagging was not occurring during the interval examined.