Survival of Two Bacterial Fish Pathogens (Aeromonas salmonicida and the Enteric Redmouth Bacterium) in Ozonated, Chlorinated, and Untreated Waters

Abstract

O3 and Cl inactivation curves were determined in 3 water types at 20.degree. C for the destruction of the fish pathogens, A. salmonicida, the etiologic agent of furunculosis, and the enteric redmouth bacterium (ERM). In phosphate-buffered distilled water, 0.01 mg/l ozone inactivated 103 cells/ml of ERM and A. salmonicida in 1/2 and 10 min, respectively. Cl at this concentration had little effect on either pathogen and a residual of at least 0.05 mg/l was needed to achieve a complete kill within a 10 min contact time. In soft lake water (30 mg/l as CaCO3) a Cl residual of 0.1 mg/l rapidly (1/2-1 min) inactivated A. salmonicida and ERM but in hard water (120 mg/l) A. salmonicida was more resistant and 0.2 mg/l Cl was required. Ozonation of the 2 lake waters at 90 mg O3 .cntdot. h-1 .cntdot. l-1 (equivalent to a 0.01 mg/l residual in ozone demand-free water) was required to destroy both pathogens within 10 min. In untreated soft lake water 103 cells/ml of A. salmonicida survived only 2 days, while the ERM bacterium (103 cells/ml) survived even after 20 days in soft and hard untreated lake waters.