The pathology and pathophysiology of bacterial kidney disease and the interactive effects of smoltification on the development of bacterial kidney disease in steelhead trout (Oncorhynchus mykiss)
Abstract
Based on circumstantial evidence, it was believed that recently released salmonids from public and private hatcheries were dying from bacterial kidney disease (BKD) and the reason for the decline in the salmonid populations in Lake Michigan. It was further proposed that the salmonids were dying from BKD because they were released during smoltification. The relationship between BKD and smoltification has not been evaluated in a controlled setting. In addition, previous experimental studies of BKD did not adequately reproduce the disease and the pathophysiology of the disease is poorly understood. Laboratory-acclimated steelhead trout were inoculated with BKD as parr and were terminally sampled as the population underwent smoltification. Additional steelhead trout were inoculated as parr or as smolts. The smolt status was established in the steelhead trout using computer-assisted morphometry. The induced disease in the steelhead trout reflected the natural disease (systemic granulomatous disease). Previous pathophysiology studies demonstrated that BKD induced anemia. The cause for the anemia was proposed to be due to hemolysis, hemorrhage, splenic congestion, liver failure or necrosis of hematopoietic tissues. It was also concluded that alterations in serum biochemistry profiles in R. salmoninarum -infected salmonids were due to liver or kidney failure. Our results indicate that the anemia may be due to a shortened half-life of erythrocytes due to damage induced by the granulomatous inflammation associated with blood sinuses and due to the effacement of hematopoietic tissues by inflammation. The alterations in serum biochemistry profiles reflect an inflammatory reaction and alterations in metabolism. No significant differences in gross or histologic lesions, bacterial protein concentration (kidney tissues), hematologic profiles, serum biochemistry profiles or cortisol levels were detected between the R. salmoninarum-infected parr, transients or smolts or between the steelhead trout inoculated as parr versus those inoculated as smolts. These results indicate that smoltification does not play a significant role in the development of BKD in laboratory-acclimated steelhead trout. Other factors, such as the environmental changes that occur at the time of smoltification or the stress associated with migration, may play a more significant role in the development of BKD in recently released salmonids than smoltification.
Degree
Ph.D.
Advisors
Thacker, Purdue University.
Subject Area
Veterinary services|Aquaculture|Fish production|Animal diseases
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.