The toxicity of chlorine dioxide to clownfish and its bactericidal capability to pathogenic strains of vibrio spp.

Abstract

Global ornamental fish transportation ranging from hours to days can produce multiple stress factors impact fish health and cause mortality. Clownfish, particularly Amphiprion ocellaris, are among the most traded saltwater ornamental fish. Vibrio includes several pathogenic strains that affect aquatic animals. Consequently, prophylactic treatment of the water or fish is recommended. In this study, six Vibrio strains including V. alginolyticus, V. parahaemolyticus and V. harveyi isolated from sick A. ocellaris and one V. harveyi strain from a sick East Asian fourfinger threadfin (Eleutheronema rhadinum) were tested for their sensitivity to a popular disinfectant, chlorine dioxide (ClO₂). The results showed that 0.25 ppm ClO₂ effectively suppressed five of the seven tested Vibrio strains for 24 h; however, 0.1 ppm ClO₂ is safer for A. ocellaris. Meanwhile, ClO₂ 2.5 ppm reduced the bacterial counts to below 3.3 × 10⁵ CFU/mL for 24 hours. The LC₅₀ of ClO₂ for A. ocellaris was 0.87 ppm at 10 min and 0.72 ppm at 24 h post treatment. Mild changes in water quality, including dissolved oxygen (DO), temperature and pH, were recorded during the trial. More research is necessary to understand the sensitivity of various aquatic animal pathogens to ClO₂ and its toxicity to different aquatic animals.