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 alevins after injecting antibiotics into pre-spawning female salmon (O. kisutch) and to evaluate if this was an effective means of controlling vertical transmission of R. salmoninarum (Rs), the causative agent of bacterial kidney disease. Five antibiotics (erythromycin phosphate, penicillin G, oxytetracycline, cephradine, and rifampicin) were injected into the 'dorsal sinus' of maturing female coho salmon, one antibiotic per fish, 2 to 3 wk before spawning. Eggs from these fish were then infected internally with Rs using a microinjection technique. The prevalence of the resulting infections was determined for the eggs at the eyed stage and for alevins at hatch. Concentrations of each antibiotic were measured in the egg yolk at spawning and in the alevins at hatch. All 5 antibiotics were detected in eggs taken at spawning, but only erythromycin and rifampicin were present in measurable amounts within the alevins at hatch. The 5 antibiotics all proved to be effective in significantly reducing the prevalence of Rs infections of the hatch stage. The broodstock injection technique therefore appears to be a promising means of reducing the vertical transmission of Rs.