Hatchery Evaluation of Erythromycin Phosphate Injections in Prespawning Spring Chinook Salmon

Abstract

Abstract In a hatchery field trial, we evaluated the efficacy and safety of two sequential injections of erythromycin phosphate in prespawning spring chinook salmon Oncorhynchus tshawytscha. For dosing purposes, we used fish fork length to estimate weight based on a weight−length relationship for spring chinook salmon. All fish in the hatchery population (N = 1,568) were injected with one of two doses of erythromycin phosphate (20 mg/kg body weight or 40 mg/kg), followed 1 month later by a second injection of 20 mg/kg. We monitored the survival of fish after injection and determined the concentrations of erythromycin and soluble antigen of Renibacterium salmoninarum in the kidneys of each fish that survived to spawning. After the first injection, mortality was significantly higher among female fish administered 40 mg/kg than among female fish administered 20 mg/kg. The concentration of erythromycin in the kidneys of females at spawning was significantly higher than that in the kidneys of males, as was the...