Fish Pathology
Online ISSN : 1881-7335
Print ISSN : 0388-788X
ISSN-L : 0388-788X
Current issue
Displaying 1-8 of 8 articles from this issue
Review
  • Kazuo Ogawa
    Article type: Review
    2023 Volume 58 Issue 4 Pages 127-145
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    Amberjacks of the genus Seriola (Japanese amberjack S. quinqueradiata, greater amberjack S. dumerili and yellowtail amberjack S. aureovittata) are most important fish resources, caught and cultured in Japan. ​Eight species of parasites are known to infect the skeletal muscle of Japanese Seriola spp.: the microsporidian Microsporidium seriolae, the myxozoans Kudoa amamiensis, Kudoa megacapsula and Unicapsula seriolae, the digenean Hirudinella ventricosa, the cestode Protogrillotia zerbiae and the nematodes Philometroides seriolae and Anisakis pegreffii. ​They induce detrimental effects on the quality of the muscle tissue and lower marketable value due to anesthetic appearances. ​Additionally, U. seriolae and A. pegreffii may cause food poisoning and zoonosis, respectively. ​In this paper, literature of these parasites from wild and cultured Seriola spp. is reviewed, and current status of their studies and issues are discussed.

    Download PDF (1586K)
Research Articles
  • Takayuki Minami, Terutoyo Yoshida, Issei Nishiki
    Article type: Research Article
    2023 Volume 58 Issue 4 Pages 146-152
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    Mortalities due to Lactococcus garvieae-like infection have been observed in farmed greater amberjack Seriola dumerili previously immunized with a commercial L. garvieae vaccine containing serotype I and II strains in Miyazaki Prefecture since August 2021. ​The isolates from diseased fish were not agglutinated by the anti-serotype I and II sera, and showed genetic similarity to L. garvieae serotype I in multi-locus sequence (16S rRNA gene, pheS, recA, rpoA and rpoB) analysis. ​The pathogenicity of isolates was confirmed by intraperitoneal injection in greater amberjack, and the lethal dose fifty was less than 1.6 × 103 CFU/FISH. ​In a vaccine trial, greater amberjack, which had been immunized with formalin-killed cells (FKC) prepared from both serotype I and II strains, was not effectively protected against an isolate from this study, whereas those immunized with FKC prepared using the isolate were effectively protected against the infection with an isolate exhibiting the same antigenicity. ​Based on these findings, we propose a new serotype: serotype III, which is not agglutinated with both anti-serotype I and II serum and not protected against a serotype I and serotype II-combined vaccine.

    Download PDF (1444K)
  • Norihisa Oseko
    Article type: Research Article
    2023 Volume 58 Issue 4 Pages 153-163
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    Flavobacterium psychrophilum, the causative agent of bacterial cold-water disease, was first reported in spawning chum salmon Oncorhynchus keta in Hokkaido in 2005. ​In the present study, Hokkaido was divided into five regions by chum salmon stock, and the distribution of this bacteria in spawning chum salmon and the other three species of salmonid fish that return to rivers in each region​—masu salmon O. masou, pink salmon O. gorbuscha, and sockeye salmon O. nerka—was surveyed over a three-year period from 2006 to 2008. ​Samples were collected from the ovarian fluid and kidneys of female salmon, and in some rivers, milt from males was also sampled. ​F. psychrophilum was detected in all rivers surveyed in all regions, and in males and females of all four spawning salmon species. ​The detection rates were high in many rivers (> 70%). ​These results confirm that the pathogen is widespread in Hokkaido regardless of stock, species, or sex of salmons. ​Furthermore, PCR-RFLP genotyping of pathogen isolates from chum salmon revealed multiple genotypes in some rivers. ​In these rivers, the pathogen was thought to have invaded early and differentiated, or to have invaded as multiple strains with different genotypes.

    Download PDF (750K)
  • Hajime Arai, Shun Watanabe, Shotaro Izumi
    Article type: Research Article
    2023 Volume 58 Issue 4 Pages 164-170
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    In Japan, Bacterial cold-water disease (BCWD) is an economically important fish disease, occurring in ayu Plecoglossus altivelis altivelis not only at aquaculture farms but also in rivers. ​In this study, an epizootiological study of BCWD was conducted to understand the route of infection in ayu and the source of the causative agent, Flavobacterium psychrophilum in rivers. ​We used a genotyping system with a combination of four PCR-restriction fragment length polymorphisms (PCR-RFLP). ​For five years from 2014 to 2018, various fish, mainly ayu, were caught and sampled in the Kanna River, Gunma Prefecture, Japan. ​A total of 852 isolates of F. psychrophilum from these fish species were used as PCR-RFLP genotyping samples. ​Nine PCR-RFLP genotypes were identified among these isolates, some of which were the typical epizootic types for ayu in this river, while species-specific genotypes exist in other fish species. ​In addition, fish species other than ayu, decoy ayu, and land-locked ayu were suspected as reservoirs of epizootic F. psychrophilum genotypes for ayu in the Kanna River. ​These results provide the basis for an epizootiological assessment of the transmission dynamics of ayu BCWD not only in the Kanna River but also in rivers in general.

    Download PDF (551K)
Short Communications
  • Hirotaka Katahira, Orie Ikeda, Taiga Yodo
    Article type: Short Communication
    2023 Volume 58 Issue 4 Pages 171-174
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    An outbreak of ectoparasitic copepods occurred on the Japanese rice fish Oryzias latipes stocked in an outdoor tank for the extraterritorial conservation program. ​Only the adult female copepods were found on the skin and fins of the host fish. ​The parasite was identified as Neoergasilus japonicus from the morphological characters including an inflated projection on the second segment of the exopod of the first swimming leg, and the single-segmented exopod and endopod of the fourth leg. ​Partial sequence of 28S rDNA and cox1 genes also supported the morphological identification. ​This is a new host record for N. japonicus. ​A bath treatment with 1% salt concentration was effective in detaching the parasite within a day.

    Download PDF (1267K)
  • Aki Nishihara, Takechiyo Sumiyoshi, Koushiro Arakawa, Natsuki Morimoto ...
    Article type: Short Communication
    2023 Volume 58 Issue 4 Pages 175-179
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    Edwardsiella bacteria infect Japanese medaka Oryzias latipes; however, the difference in susceptibility between E. piscicida and E. anguillarum is unknown. ​In this study, we performed challenge tests with medaka using four Edwardsiella strains, which were difficult to be identified by specific primers. ​The four strains were reclassified as three E. piscicida strains and one E. anguillarum strain using phylogenetic analysis. ​The immersion challenge demonstrated that medaka were more susceptible to E. piscicida than to E. anguillarum. ​Increases in the bacterial copy number in the infected medaka kidneys were correlated with the worsening of the external symptoms. ​Medaka is considered a valuable model organism for understanding the etiology of edwardsiellosis.

    Download PDF (1126K)
  • Soetsu Yanagi, Yoshiaki Imaoka, Kazuo Ogawa
    Article type: Short Communication
    2023 Volume 58 Issue 4 Pages 180-183
    Published: December 15, 2023
    Released on J-STAGE: January 09, 2024
    JOURNAL RESTRICTED ACCESS

    Wild, one-year yellowtail amberjack Seriola aureovittata (n = 13) were examined for parasites after about one month culture in Nagasaki and Kagoshima Prefectures, Japan. ​All fish were infected with the microsporidian Microsporidium seriolae (all qPCR positive; 11 with cysts in the skeletal muscle, four with cysts in the heart as well). ​Considering fish size, culture period, and time required for cyst formation, it is assumed that the fish had been infected with the microsporidian in the wild. ​Additionally, two fish were infected with a nematode in the skeletal muscle, tentatively identified as Philometroides seriolae, which had been recorded only from S. quinqueradiata.

    Download PDF (761K)
Information
feedback
Top