Distribution of a fish pathogen Listonella anguillarum in the Japanese flounder Paralichthys olivaceus hatchery

The present study was undertaken to investigate the distribution of Listonella anguillarum in a Japanese flounder (Paralichthys olivaceus) hatchery. A total of 2704 isolates were obtained from the developing fish, live diets and artificial feeds of Japanese flounder and their rearing water, 439 of which were identified as L. anguillarum by the combining incubation on thiosulfate-citrate-bile salt-sucrose (TCBS) agar at 35 degrees C overnight with polymerase chain reaction (PCR) detection for the VAH1 hemolysin gene. L. anguillarum was detected in all seven rotifer samples, with densities of 2.5 x 10(3) to 4.6 x 10(6) colony forming units (CFU) g(-1). Both the analyzed samples of Nannochloropsis oculata contained this bacterium at densities of 1.6 x 10(4) to 1.4 x 10(5) CFU g(-1). L. anguillarum was detected in only one of four samples of Artemia nauplii with a density of 4.8 x 10(5) CFU g(-1) (35%) and it was not detected in the two analyzed artificial feed samples. L. anguillarum was detected in I I of 18 specimens of larval and juvenile Japanese flounder at densities of 5.0 x 10(1) to 7.4 x 10(5) CFU g(-1), while it was not detected in the two analyzed egg specimens of Japanese flounder. These results indicate that L. anguillarum associated with the developing Japanese flounder is likely derived from rearing water and live diets such as rotifers. Further, it is strongly suggested that L. anguillarum is a transient bacterium of the intestinal microflora for the Japanese flounder but is a permanently indigenous one for the Japanese flounder hatcheries. (c) 2006 Elsevier B.V. All rights reserved.