Isolation and Characterization of Vibrio kanaloae as a Major Pathogen Associated with Mass Mortalities of Ark Clam, Scapharca broughtonii, in Cold Season

Abstract

High temperature is a risk factor for vibriosis outbreaks. Most vibrios are opportunistic pathogens that cause the mortality of aquatic animals at the <i>vibrio</i> optimal growth temperature (~25 °C), whereas a dominant <i>Vibrio kanaloae</i> strain SbA1-1 is isolated from natural diseased ark clams (<i>Scapharca broughtonii</i>) during cold seasons in this study. Consistent symptoms and histopathological features reappeared under an immersion infection with SbA1-1 performed at 15 °C. The pathogenicity difference of SbA1-1 was assessed under different temperatures (15 °C and 25 °C). The cumulative mortality rates of ark clams were significantly higher at the low temperature (15 °C) than at the high temperature (25 °C); up to 98% on 16th day post SbA1-1 infection. While the growth ratio of SbA1-1 was retarded at the low temperature, the hemolytic activity and siderophores productivity of SbA1-1 were increased. This study constitutes the first isolation of <i>V. kanaloae</i> from the natural diseased ark clams (<i>S. broughtonii</i>) in cold seasons and the exposition of the dissimilar pathogenicity of SbA1-1 at a different temperature. All the above indicates that <i>V. kanaloae</i> constitutes a threat to ark clam culture, especially in cold seasons.