Appraisal of Recommendations For Disinfecting Eggs Of Atlantic Salmon (Salmo salar) In Iodophor     Rocco C. Cipriano,1* Bernard M. Novak, 2 Daniel E. Flint2, and Darleen C. Cutting3   1USGS, National Fish Health Research Laboratory, 11700 Leetown Road, Kearneysville, WV; 2 USFWS, Richard Cronin National Salmon Station, 51 East Plumtree Road, Sunderland, MA; 3USFWS, Connecticut River Coordinator’s Office, 103 East Plumtree Road, Sunderland, MA   The federal protocol, which requires disinfection of fish eggs in 50-mg/L of iodine for 30 min followed by a secondary disinfection in 100-mg/L iodine for 10 min, was investigated through six spawns of Atlantic salmon (Salmo salar) at the Richard Cronin National Salmon Station (Sunderland, MA).  These salmon had undergone an epizootic of furunculosis and the surviving fish maintained a persistent infection of A. salmonicida throughout the course of study.  Eggs from twenty paired-matings of salmon were obtained annually from 1995 through 2000, except for 1999 when eggs from 35 pairs of salmon were examined.   Aeromonas salmonicida was isolated from 19 of 135 total groups of fertilized eggs that were investigated throughout this study.   In these cases, all isolations of the pathogen were made only from fertilized eggs before any disinfection in iodophor had occurred.    Results also provided further evidence that A. salmonicida is not transmitted vertically via intra-ovum infection.  In contrast to our field results, in vitro assays actually showed that A. salmonicida was incompletely killed when concentrations of the bacterium ranged between 1.0x107 to 1.2x108 cfu/mL. However, even when bacterial concentrations exceeded 1.0x107 cfu/mL no A. salmonicida remained viable if treated first with 50-mg/L iodine for 30 minutes and then with 100-mg/L iodine for 10 minutes, as prescribed by federal policy.  Incomplete disinfection of A. salmonicida at cell densities greater than or equal to 1.0x107 cfu/mL in either 50 mg/L iodophor for 30 minutes or in 100 mg/L iodophor for 10 minutes was observed only in A-layer positive phenotypes of cloned isolates.  Isogenic A-layer negative clones, as well as representative ten strains of Yersinia ruckeri and Aeromonas hydrophila were completely disinfected using a single treatment with either 50 mg/L iodophor for 30 min or 100 mg/L iodophor for 10 min.  At high bacterial concentrations, more bacterial clumps are produced by A-layer positive phenotypes of A. salmonicida.  We speculate that the outer cells of these clumps may “shield” and protect a small percentage of cells at the core of the clump, which produces an incomplete disinfection.