Effect of common aquaculture chemicals against Edwardsiella ictaluri and E. tarda

Edwardsiellosis is an important bacterial infection of freshwater and marine fishes. Edwardsiella ictaluri causes enteric septicemia of catfish, and E. tarda causes emphysematous putrefactive disease of catfish and fish gangrene in various species; these diseases have considerable economic effects on the aquaculture industry. In addition, E. tarda is an important zoonotic pathogen. Thus, the reduction or elimination of these pathogens from an aquarium or aquaculture facility is imperative. This study examined a variety of commercially available chemicals for their ability to reduce or eliminate E. ictaluri and E. tarda from the aquatic environment. The various concentrations of chemicals were tested in vitro in microcentrifuge tubes with a known concentration of bacteria at room temperature. In this study, ethyl alcohol (30, 50, or 70%), benzyl-4-chlorophenol/phenylphenol (1%), sodium hypochlorite (50, 100, 200, or 50,000 mg/L), n-alkyl dimethyl benzyl ammonium chloride (1:256), povidone iodine (50 or 100 mg/L), glutaraldehyde (2%), and potassium peroxymonosulfate/sodium chloride (1%) were effective disinfectants, as each reduced or eliminated the number of detectable organisms within 1 min of contact time. However, neither Chloramine-T (15 mg/L) nor formalin (250 mg/L) substantially reduced bacterial counts even after 60 min of contact time.