Isolation and characterization of pathogenic Vibrio harveyi (V-carchariae) from the farmed marine cobia fish Rachycentron canadum L. with gastroenteritis syndrome

摘要

An outbreak of serious mortality among the cultivated juvenile cobia Rachycentron canadum L. (weighing 8-10 g) characterized by a swollen intestine containing transparent yellow fluid (ascites and gastroenteritis) occurred in August 2001 in Taiwan. Ten motile bacterial strains, C3d1-C3d10, were isolated from head kidney (an organ located near the head of the fish) and/or the intestinal yellow fluid on tryptic soy agar supplemented with 1% NaCl (TSA1) and/or thiosulphate citrate bile salt sucrose (TCBS) agar plates. These strains were characterized and identified as Vibrio harveyi (V. carchariae) on the basis of biochemical characteristics, and comparisons with those of three reference strains, originally identified as V. harveyi or V. carchariae. The strain C3d1 was selected as a representative strain for virulence tests and was found lethal to the cobia with an LD50 value of 7.48 x 10 4 colony forming units g(-1) fish body weight. All the moribund/dead fish exhibited gastroenteritis as that observed in natural outbreak. The same bacteria could be reisolated from kidney and the transparent yellow fluid of swollen intestine of fish after bacterial challenge using TSA1 and TCBS plates. This is a first report showing that V. harveyi (V. carchariae) is the causative agent of gastroenteritis in the cobia. [References: 29]