Use of Penicillin and Streptomycin to Reduce Spread of Bacterial Coldwater Disease I: Antibiotics in Sperm Extenders

Abstract Bacterial coldwater disease caused by Flavobacterium psychrophilum has led to the loss of significant numbers of hatchery‐reared salmonids. The bacteria can be spread from parent to progeny within contaminated sperm and ovarian fluid. Methods for disinfecting ovarian fluid and unfertilized eggs are available, but methods for disinfecting sperm have not been described. In this study we determined whether sperm extenders containing a mixture of penicillin and streptomycin can be used to eliminate F. psychrophilum . In vitro trials demonstrated that when Rainbow Trout Oncorhynchus mykiss sperm is mixed with an extender, a 15‐min exposure to 0.197 mg penicillin plus 0.313 mg/mL streptomycin is effective at killing the bacteria and has no effect on sperm motility. Small‐scale trials showed that egg fertilization rates were not reduced when sperm held in an extender solution containing the same antibiotic mixture for 15 min was used to fertilize eggs. Production‐scale trials, however, showed a roughly 18% decrease in egg fertilization rate when sperm stored in an antibiotic containing extender was used. To determine why a reduction in fertilization capacity was observed, a small‐scale experiment testing the fertilization of eggs with larger quantities of sperm was performed and showed that increasing the volume of sperm used did not increase fertilization rates. Our results demonstrate that extenders containing penicillin and streptomycin can be used to disinfect sperm, especially when small quantities of eggs are fertilized, but factors negatively affecting egg fertilization and survival on a production scale still need further investigation. Received May 1, 2014; accepted August 10, 2014