Concentrations of Erythromycin in Maturing Chinook Salmon after Intraperitoneal Injection of One of Two Drug Formulations

Abstract

A dose (10 mg/kg) of erythromycin phosphate or erythromycin base was injected intraperitoneally into maturing spring chinook salmon Oncorhynchus tshawytscha on one of three dates before sexual maturity to observe if differences in the concentrations of erythromycin remaining in tissues 14 d after injection could be attributed to the sex of fish, drug formulation, or timing of injection. No differences due to formulation of erythromycin or date of injection were detected in kidneys or spleens, but females injected with erythromycin phosphate had significantly higher levels of erythromycin/mL in the maturing ova than did fish injected with erythromycin base. Mean concentration of erythromycin in kidneys of fish was 1.6 μg erythromycin/g wet weight. Thirty-six of 37 females and 18 of 29 males had detectable erythromycin in the spleens. Only six fish had detectable erythromycin in the liver, and no muscle tissues collected had detectable erythromycin.