Use of erythromycin in reducing vertical transmission of bacterial kidney disease

Studies were conducted in 1980-1982 to determine uptake and retention of erythromycin when eggs of chinook salmon (Oncorhynchus tshawytscha) were water hardened for 1 hr in 2 ppm of the antibiotic as a means of preventing vertical transmission of bacterial kidney disease (BKD). Although eggs absorbed up to 1 ppm during water hardening, they retained the drug less than 24 hr. Injection of adult female chinook salmon with 11 mg of erythromycin/kg of body weight to prevent prespawning mortality from BKD resulted in deposition of drug in the eggs. Erythromycin persisted in the eggs at concentrations up to 0.6 ppm for 30 to 60 d postinjection--a period that would allow prolonged contact of drug with the causative agent of BKD, Renibacterium salmoninarum. Injection of prespawning female chinook salmon with erythromycin seemingly is potentially more effective than the water hardening of eggs in erythromycin in preventing vertical transmission of BKD.