Isolation and characterization of pathogenic Vibrio alginolyticus from diseased postlarval abalone, Haliotis diversicolor supertexta (Lischke)

Outbreaks of serious mortality among cultured abalone postlarvae have occurred across Southern China since July 2002. Five motile bacterial strains were isolated from diseased abalone postlarvae on tryptic soy agar supplemented with 1% NaCl (TSA1) and/or thiosulphate citrate bile salt (TCBS) sucrose agar plates during an outbreak in August 2003 in Shanwei, Guangdong province. All isolates were characterized and identified as Vibrio alginolyticus on the basis of biochemical characteristics and comparisons with those of the reference strain V. alginolyticus ATCC 17749. Strain 19 (a representative of five similar isolates) was virulent to abalone postlarvae with an LD₅₀ value of1.00 × 10⁴ colony‐forming units mL^?1. All abalone postlarvae exhibited the same signs as in natural outbreaks. The same bacterium could be re‐isolated from abalone postlarvae after bacterial challenge using TSA1 and TCBS plates. The results reveal that V. alginolyticus is an infectious agent of abalone postlarvae.