Effect of Copper Sulfate on Aeromonas hydrophila Infection in Channel Catfish Fingerlings

Abstract

AbstractMotile Aeromonas septicemia results from primary or secondary infection with bacteria from Aeromonas spp., including Aeromonas hydrophila. Since 2009, an emerging strain of A. hydrophila has been associated, as a primary pathogen, with significant morbidity and mortality in the U.S. catfish industry. Two 2 × 2 factorial experiments with five replicates were conducted to evaluate whether copper sulfate pentahydrate (CuSO4) at a concentration of 1% of total alkalinity (total alkalinity = 98 mg/L as CaCO3; total hardness = 60 mg/L as CaCO3; pH = 7.4) can reduce mortality of channel catfish Ictalurus punctatus after their exposure to this emerging strain of A. hydrophila. In experiment 1, fingerling channel catfish received an 18‐h continuous bath exposure to CuSO4 after A. hydrophila challenge. Survival in the treatments challenged with A. hydrophila, both when exposed or unexposed to CuSO4, was significantly lower than survival in sham‐exposed controls. Fish exposed to A. hydrophila and treated with copper sulfate had the lowest percent survival, at 18% (SE, 7.0), and survival was significantly different from the treatment in which fish were exposed to A. hydrophila but not treated with copper sulfate. In experiment 2, fish received a 4‐h pretreatment with CuSO4 before exposure to A. hydrophila plus a 4‐h treatment the next day. In experiment 2, when fish were exposed to A. hydrophila but not CuSO4, survival was 80.0% (SE, 5.5). For fish exposed to A. hydrophila and to CuSO4, survival was 50.0% (SE, 3.2). The percent mortality in the treatment exposed to A. hydrophila and to CuSO4 was signficantly different from all of the other treatments. This study demonstrated that, under these experimental conditions, CuSO4 application reduced survival when used as a treatment for infection of fingerling channel catfish with this strain of A. hydrophila.