Susceptibility and clearance of Aeromonas salmonicida (furunculosis) in Coregonus artedi (lake herring)

Aaron Cupp (USGS, acupp@usgs.gov), James Luoma (USGS), Maren Tuttle-Lau (USFWS), Eric Leis (USFWS)

Aquaflor® (florfenicol) and Terramycin®200 for Fish (oxytetracycline) are approved medications in the United States for delivery with feed to control mortality in salmonids due to furunculosis associated with Aeromonas salmonicida. The purpose of this study was to validate the efficacy of florfenicol and oxytetracycline medicated feeds to treat A. salmonicida infected Lake Herring (Coregonus artedi) to inform U.S. Fish and Wildlife Service staff overseeing the ongoing Coregonid propagation efforts. Lake Herring were subjected to static infection baths containing A. salmonicida or a sham control and then distributed to replicate test tanks within four treatment groups: (1) fish infected with A. salmonicida and treated with 15 mg florfenicol/kg body weight (BW)/d, (2) fish infected with A. salmonicida and treated with 83 mg oxytetracycline/kg BW/d, (3) fish infected with A. salmonicida and treated with a non-medicated control, and (4) uninfected fish treated with a non-medicated control. Medicated and comparative non-medicated feed rations were administered at 2% BW/d for 10 consecutive days in accordance with the U.S. Food and Drug Administration approved drug label followed by 7-d post-dosing observation period using only non-medicated feed. Lake Herring infected with A. salmonicida that were treated with florfenicol (79% survival) and oxytetracycline (85% survival) had significantly higher survival than fish infected with A. salmonicida that received no medicated treatment (3% survival). No statistical difference in survival between the two medicated feed types was found. Aeromonas salmonicida was not detected in the kidney tissue of any surviving fish treated with medicated feeds at 7-d post-dosing using quantitative qPCR analysis. Overall, this study demonstrated that florfenicol and oxytetracycline medicated feeds were effective A. salmonicida treatments for Lake Herring for the conditions and fish sizes that were tested.