ESTABLISHMENT OF A NEGATIVE-POSITIVE THRESHOLD OPTICAL-DENSITY VALUE FOR THE ENZYME-LINKED-IMMUNOSORBENT-ASSAY (ELISA) TO DETECT SOLUBLE-ANTIGEN OF RENIBACTERIUM-SALMONINARUM IN ALASKAN PACIFIC SALMON

Kidney tissues from 5231 chinook salmon Oncorhynchus tshawytscha and 3 793 coho Salmon O. kisutch adults used for spawning were examined for soluble antigen of Renibacterium salmoninarum (Rs) by the enzyme-linke d immunosorbent assay (ELISA). The purpose of this study was to develo p an extensive data base for establishing a negative-positive threshol d optical density value for Rs-negative and -positive fish using comme rcially available ELISA reagents. Statistical evaluation of the estima ted distribution of Rs-negative optical density values from coho and c hinook salmon indicated the preliminary estimated negative-positive th reshold value of 0.1 was not conservative enough, i.e. there was an un acceptably high probability that a large number of low-level Rs-positi ve fish were not identified. Consequently, a more conservative thresho ld value of 0.095 was chosen that erred in identifying dn acceptably l ow number of negative fish ds positive. At this threshold optical dens ity value the ELISA could detect about 20 ng of Rs antigen ml-1 of kid ney homogenate.