Prevention of Flavobacterium psychrophilum Vertical Transmission by Iodophor Treatment of Unfertilized Eggs in Salmonids Akira

We evaluated the eficacy of povidone-iodine treatments in preventing vertical transmission of Flavobacterium psychrophilum in the eggs of masu salmon Oncorhynchus masou, Japanese char Salvelinus pluvius, coho salmon O. kisutch and rainbow trout O. mykiss. When newly spawned eggs were immersion-chalenged with F. psychrophilum (> 10 CFU/mL) and subsequently disinfected with povidone-iodine (50 ppm in PBS, 15 min) prior to fertilization, the pathogen was not detected in the contents of the eggs. Without this pre-fertilization disinfection with povidone-iodine, however, procedures such as water-hardening of immersion-chalenged eggs in povidone-iodine (50–100 ppm in water) and rinsing of the F. psychrophilum-contaminated eggs with PBS were insuficient to control the intraovum infection. In a separate experiment using coho salmon eggs chalenged with F. psychrophilum, pre-fertilization disinfection was efective to prevent bacterial cold-water disease in the produced fry. Surface disinfection of unfertilized eggs immediately after spawning is thus essential to prevent vertical transmission of F. psychrophilum.