MONITORING FOR EARLY DETECTION OF AEROMONAS-SALMONICIDA TO ENHANCE ANTIBIOTIC-THERAPY AND CONTROL FURUNCULOSIS IN ATLANTIC SALMON

Juvenile Atlantic salmon Salmo salar at the White River National Fish Hatchery were monitored quarterly for Aeromonas salmonicida, the etiol ogic agent of furunculosis. Samples were obtained in August, November, January, and March, within an 8-month smelt production cycle during 1 992-1993. Aeromonas salmonicida was isolated in August from external m ucus and kidneys of fish within six production pools, each containing about 7,500 fish. Topical disinfection with a 60-min bath of Chloramin e-T at 15 mg/L on three consecutive days did not control the prevalenc e of infection. Atlantic salmon were then fed 77.0 mg of oxytetracycli ne per kilogram of fish for 10 d. Mortality subsided in all tanks with in 4 d after initiation of oral antibiotic therapy. Further examinatio n failed to isolate the pathogen 21 d after cessation of treatment. In November, A. salmonicida was detected in the mucus of one fish from a single tank; treatment was not prescribed. Pathogens were not detecte d shortly after fish were marked with coded wire tags in January or pr ior to release in March. Monitoring programs allowed early detection o f the pathogen; this led to treatment that permitted fish to be stocke d in accordance with established fish health policy regulations for sa lmonids in New England.