Transmission of Bacterial Kidney Disease from Wild to Stocked Hatchery Trout

Natural, horizontal transmission of bacterial kidney disease (BKD) from infected wild brook trout (Salvelinus fontinalis) to newly stocked hatchery brook trout, brown trout (Salmo trutta), and rainbow trout (Salmo gairdneri) was shown in a small lake and stream system in southeastern Wyoming, USA. Stocked trout were infected naturally and died in 9 mo or less after exposure to infected wild fish. Dead and live fish collected from each of three stations were necropsied. Fluorescent antibody techniques (FAT) were used to detect the BKD organism in all samples. Low severity infections were often detected by FAT at a higher rate when feces were examined as compared to kidney tissues from the same fish. Because other known pathogens were essentially absent, BKD was diagnosed as the cause of all deaths in both stocked hatchery fish and wild fish. Rainbow trout were found to be the most refractory species.Key words: bacterial kidney disease, natural disease transmission, wild trout, brook trout, brown trout, rainbow trout, epizootics