COMPARISON OF DIAGNOSTIC-TESTS FOR BACTERIAL KIDNEY-DISEASE IN JUVENILE STEELHEAD TROUT (ONCORHYNCHUS-MYKISS)

In order to accurately diagnose bacterial kidney disease caused by Ren ibacterium salmoninarum in steelhead trout, kidney tissue from experim entally infected fish was evaluated using a commercially available enz yme-linked immunosorbent assay (ELISA) test kit, fluorescent antibody (FA) testing, bacteriologic culture, and histopathology. Seventy-five steelhead trout were randomly assigned to 1 of 4 groups and intraperit oneally inoculated with 0.15 ml saline (n = 20), 1 x 10(10) organisms/ ml (n = 18), 1 x 10(8) organisms/ml (n = 18), or 1 x 10(6) organisms/m l (n = 19) of R. salmoninarum. ELISA, FA, and bacteriologic culture we re positive for R. salmoninarum from the kidney tissue of the 2 groups infected with the highest doses. Although the ELISA and FA tests were accurate when compared to the bacteriologic culture from the 2 groups infected with the higher doses of the organism, they were less sensit ive at the lowest level of inoculum. Histopathology was not specific f or this disease; however, all infected fish had a marked proliferative histiocytic interstitial nephritis, characterized by marked expansion of the renal hematopoietic tissue by histiocytes without tissue necro sis. Other microscopic findings included splenitis and myositis (at th e injection site) of some fish.