A new species, Vibrio trachuri sp. nov., was isolated from the cultured Japanese horse mackerel (Trachurus japonicus). These Vibrio were Gram negative, motile rods and formed yellow colonies on BTB teepol and TCBS plate, turned TSI medium to yellow and was sensitive to 150 μM O/129 (2,4‐diamino‐6,7‐diisopropyl pteridine phosphate) like Listonella anguillarum which has been described as Vibrio anguillarum. However, the results of VP test and decarboxylation of lysine or dihydrolation of arginine suggested that these Vibrio are rather closely related to V. parahaemolyticus. DNA similarity determined by the microplate hybridization technique revealed that these Vibrio are genetically quite distant from Listonella anguillarum or V. parahaemolyticus and rather close to V. harveyi, although there was no Vibrio species which had more than 70% similarity value. From these results we propose to nominate Vibrio trachuri sp. nov. for this new Vibrio species.

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A polymerase chain reaction (PCR) method was performed for rapid and sensitive detection of pathogenic Vibrio trachuri isolated from cultured Japanese horse mackerel. A set of primers was selected from the base sequence of the Pst I fragment of T9210 chromosomal DNA and used for PCR detection of T9210. This PCR specifically amplified the DNAs from V trachuri T9210, T9213, and T9216 but not of those other bacterial strains. PCR using a Pst I-1 primer set made it possible to detect 100 fg of T9210 DNA. The PCR method reported here may be useful for detection and identification of V trachuri pathogenic to Japanese horse mackerel.Key words: Polymerase chain reaction, Vibrio trachuri, Japanese horse mackerel, Pst I fragment Vibriosis is one of the most serious bacterial diseases causing extensive damage to fish farms and hatcheries. Listonella anguillarum (Vibrio anguillarum) has been described as the main species causing vibriosis in fish (1). Muroga and Egusa (11) isolated pathogenic vibrios from ayu and identified them as V anguillarum. In a previous work (5) we isolated Vibrio sp. T9210, which causes vibriosis in Japanese horse mackerel, and clarified that it exhibits different biochemical characters from those of L. anguillarum which are similar to those of V parahaemolyticus (3,4,8). DNA similarity between Vibrio sp. T9210 and L. anguillarum or V parahaemolyticus as determined by fluorometric DNA-DNA hybridization (2) was also very low. From these results, we proposed nominating Vibrio trachuri as the name for this new Vibrio species. Vibrio sp. T9210, T9213, and T9216 have been deposited as JCM9677, 9678, and 9679, respectively (5).Biochemical techniques do not provide definite identification because strains vary in their phenotypic properties. Methods based on genomic analysis are more rapid and accurate. In order to determine the distribution of pathogenic V trachuri in Japanese horse mackerel farms and to prevent the spread of vibriosis, establishment of a method for rapid detection and identification of pathogenic -vibrios is necessary. The base sequence of the fur gene (9) or 16S rDNA (10) have been analyzed in V anguillarum. However, the genome of pathogenic V trachuri T9210 has not been analyzed. Therefore lengths of DNA fragments obtained by restriction enzyme treatment of chromosomal DNA were compared among Vibrio species. Some DNA fragments found only in T9210 were selected and their base sequences were determined by the dideoxy method. Primer sets composed of 20 bases each were selected and used for PCR detection of V trachuri. The specificity and the sensitivity of PCR detection were determined.Bacterial strains used in this study were the same as in our previous report. Nine L. anguillarum strains representing nine different serological groups (A-I) were from the collection of Dr. T. Aoki, Tokyo University of Fisheries. Eight strains of L. anguillarum (PT24, PT493, PT213, PB15, PB28, PT80187, PT80641, and PT80818) were isolated from ayu (Plecoglossus altivelis) and L. anguillarum ET-1 fr...

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