Control of vertical transmission of Renibacterium salmoninarum by injection of antibiotics into maturing female coho salmon Oncorhynchus kisutch

A study was conducted to evaluate the levels of drugs attained In eggs and alevlns as a result of injecting antibiotics lnto pie-spawning female salmon Oncoihynchus kisutcli and to evaluate i f thls was a n effechve means of controlling vertical transmission of Renlbacterium s a l n ~o n ~n a r u m (Rs) the causative agent of bactenal kldney disease Flve antibiotics (erythromycin phosphate penicillin G ovytetracychne cephradine and rifampicin) were ~njected into the dorsal slnus of maturing female coho salmon, one antibiotic per fish 2 to 3 wk before spawnlng Eggs from these fish were then infected ~nternally with Rs using a microinjectlon technique The prevalence of the resulting infechons was determned for the eggs at the eyed stage and for alevlns at hatch Concentrations of each antiblotlc were measured in the egg yolk at spawning and in the alemns at hatch All 5 antibiohcs were detected in eggs taken at spawning but only erythromycin and nfampicln were present in measurable amounts ~n t h i n the alevins at hatch The 5 antibiotics all proved to b e effective in significantly reducing the prevalence of Rs infections by the hatch stage The broodstock injection technique therefore appears to be a promising means of reducing the vertical transmission of Rs