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NO46 - 4

An Epidemiological Study of the Akoya Oyster Disease Using Naïve Japanese Pearl Oysters

Kazushi Odawara1*, Hirofumi Yamashita1, Kenichi Sone1,7, Hideo Aoki2, Kyoko Mori3, Shunsuke Iwanaga4,8, Chihaya Nakayasu5, Takafumi Ito5, Jun Kurita6 and Takaji Iida6
1Fisheries Research Center, Ehime Research Institute of Agriculture, Forestry and Fisheries,Ehime 798-0104, Japan
2Mie Prefecture Fisheries Research Institute, Mie 517-0404, Japan
3Fisheries Research Division, Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Oita 879-2602, Japan
4Nagasaki Prefectural Institute of Fisheries, Nagasaki 851-2213, Japan
5Tamaki Station, National Research Institute of Aquaculture Fisheries Research Agency, Mie 519-0423, Japan
6National Research Institute of Aquaculture Fisheries Research Agency, Mie 516-0193, Japan
7Ehime Prefectural Nanyo Regional Office, Department of Industry and Economy, Fisheries Division, Ehime 798-8511, Japan
8Nagasaki Prefectural Tsushima District Fisheries Extension Advisory Center, Nagasaki 817-0324, Japan
(Received July 25, 2011)

ABSTRACT―We evaluated the prevalence of the akoya oyster disease (AOD) in Japan and the pathogenicity of the unidentified causative agent. We obtained naïve Japanese pearl oysters Pinctada fucata martensii from a site with no history of AOD. In separate experiments, the oysters were either challenged by intramuscular injection with the hemolymph of infected oysters or reared in several major pearl oyster farms throughout Japan. Both groups of oysters experienced high mortality and exhibited discoloration of the adductor muscle and histopathological changes characterizing AOD. Our data suggest that AOD is prevalent in pearl oyster culture fields throughout Japan and that the causative pathogen remains highly pathogenic to P. fucata martensii. When groups of oysters produced by repeated selective breeding against AOD were reared in different pearl oyster fields alongside uninfected naïve oysters, the selectively bred oysters had significantly lower mortality than naïve oysters. The recent decline in outbreaks of AOD can be attributed, in part, to the introduction of selectively bred oysters that are resistant to this disease.

Key words: Pinctada fucata martensii, Japanese pearl oyster, akoya oyster disease, mass mortality, discoloration, histopathological change

Protective Efficacy of a Combined Vaccine against Edwardsiella tarda, Streptococcus iniae and Streptococcus parauberis in Farmed Olive Flounder Paralichthys olivaceus

Sang Yoon Han1,2, Bo Kyu Kang1, Bong Jo Kang3, Jong Man Kim1, Jee Eun Han2, Ji Hyung Kim2, Casiano Choresca Jr.2, Sang Phil Shin2, Jin Woo Jun2 and Se Chang Park2*
1Research Unit, Green Cross Veterinary Product, Yongin 227-5, Korea
2Laboratory of Aquatic Animal Medicine, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 151-742, Korea
3Ocean and Fisheries Research Institute, Jeju Special Self-Governing Province, Jeju 699-915, Korea
(Received June 22, 2011)

ABSTRACT―We evaluated the protective efficacy of a combined vaccine containing formalin-inactivated Edwardsiella tarda, Streptococcus iniae, and S. parauberis using olive flounder Paralichthys olivaceus. The fish were injected intraperitoneally with 0.1 mL of the combined vaccine. The fish were then challenged by intraperitoneal injection of the three bacterial strains. Mortality was significantly lower in the vaccinated groups compared with the control groups 3 wk post vaccination. Furthermore, there was a significant increase in antibody titer up to 16 wk after vaccination. Our results suggest that the combined vaccine successfully induced humoral and protective immunity against the three pathogens in olive flounder.

Key words: combined vaccine, protective efficacy, olive flounder, Edwardsiella tarda, Streptococcus iniae, Streptococcus parauberis

Korean and Japanese Isolates of Viral Hemorrhagic Septicemia Virus from Olive Flounder are Pathogenic to Rainbow Trout Fry

Wi-Sik Kim1, Toyohiko Nishizawa2, Jeong-Ho Kim3, Rungkarn Suebsing3, Sung-Ju Jung2 and Myung-Joo Oh2*
1The Fisheries Science Institute, Chonnam National University, Yeosu 556-901, Korea
2Department of Aqualife Medicine, Chonnam National University, Yeosu 550-749, Korea
3Faculty of Marine Bioscience and Technology, Gangneung-Wonju National University, Gangneung 210-702, Korea
(Received August 6, 2011)

ABSTRACT―We evaluated the pathogenicity of Korean and Japanese isolates of viral hemorrhagic septicemia virus (VHSV: genotype IVa) from olive flounder Paralichthys olivaceus using rainbow trout Oncorhynchus mykiss fry. The cumulative mortalities of fish challenged with FYeosu05 (Korean) and Obama25 (Japanese) isolates at 106.5 TCID50/fish were 64 and 48%, respectively. No mortality was observed among the fish challenged with either of the isolates at 105.5 TCID50/fish, or in mock-challenged fish. The affected fish exhibited darkening of the body, an expanded abdomen, pale gills, an enlarged spleen, and diffuse necrosis in the splenic and interstitial hematopoietic tissues. We re-isolated VHSV from all mortalities using cell culture and confirmed their presence by reverse transcription loop-mediated isothermal amplification (RT-LAMP). We thus concluded that Asian VHSV isolates from olive flounder are pathogenic to rainbow trout fry, although with low virulence.

Key words: Pathogenicity, viral hemorrhagic septicemia virus, genotype, Oncorhynchus mykiss, rainbow trout

Concentration of Flavobacterium psychrophilum in the Ovarian Fluid and Milt of Cultured Salmonids

Akira Kumagai1* and Akatsuki Nawata2
1Miyagi Prefecture Fisheries Technology Institute, Miyagi 986-2135, Japan
2Miyagi Prefecture Fisheries Technology Institute Freshwater Fisheries Experimental Station, Miyagi 981-3625, Japan
(Received August 10, 2011)

ABSTRACT―We measured the concentration of F. psychrophilum in the ovarian fluid and milt of six species of salmonids that were collected from freshwater fish farms in Japan. We detected the bacteria in 39 of 61 groups of female fish (544 of 3,276 fish) and 21 of 42 groups of male fish (248 of 1,434 fish). The concentration of F. psychrophilum ranged from 10 to 107.7 CFU/mL (mean 102.0 CFU/mL) in the ovarian fluid and from 10 to 104.5 CFU/mL (mean 102.1 CFU/mL) in the milt. Our data suggest that the bacteria are widely distributed, and are present at high levels, throughout Japan.

Key words: Flavobacterium psychrophilum, bacterial cold-water disease, salmonid, broodstock

Protective Efficacy of a Formalin-Killed Vaccine against Atypical Edwardsiella tarda Infection in Red Sea Bream Pagrus major

Tomokazu Takano*, Tomomasa Matsuyama, Takamitsu Sakai and Chihaya Nakayasu
National Research Institute of Aquaculture, Fisheries Research Agency, Mie 516-0193, Japan
(Received September 5, 2011)

ABSTRACT―Edwardsiella tarda causes high mortality infections in fish. To determine the efficacy of a vaccine against E. tarda, a formalin-killed preparation of atypical E. tarda FPC503 was intraperitoneally injected into red sea bream Pagrus major with or without the oil adjuvant, Montanide ISA 763 A VG. Both vaccine regimens showed protective efficacy against experimental infection with E. tarda FPC503 at 28 and 56 days post-vaccination. An enzyme-linked immunosorbent assay (ELISA) revealed the specific antibody production in vaccinated fish but the relationship between protective efficacy and antibody titer was not clear. The present results indicate that the formalin-killed vaccine is useful for the prevention of atypical E. tarda infection in red sea bream.

Key words: Edwardsiella tarda, formalin-killed vaccine, oil adjuvant, Pagrus major, red sea bream

Low Likelihood of Intra-Ovum Infection with Flavobacterium psychrophilum in Cultured Salmonids in Japan

Akira Kumagai1* and Akatsuki Nawata2
1Miyagi Prefecture Fisheries Technology Institute, Miyagi 986-2135, Japan
2Miyagi Prefecture Fisheries Technology Institute Freshwater Fisheries Experimental Station, Miyagi 981-3625, Japan
(Received September 9, 2011)

ABSTRACT―We evaluated the occurrence of intra-ovum infection with Flavobacterium psychrophilum, the causative agent of bacterial cold-water disease (BCWD) and rainbow trout fry syndrome (RTFS), in the eggs of six salmonid species in Japan. Flavobacterium psychrophilum was isolated from four eggs in one of 13 lots of eyed eggs (999 eggs) imported from the United States. In contrast, the bacterium was not isolated from 28 lots (1,680 eggs) or 61 lots (3,693 eggs) of domestically produced unfertilized or eyed eggs, respectively. Our results indicate there is a low likelihood of intra-ovum infection in cultured salmonids in Japan.

Key words: Flavobacterium psychrophilum, bacterial cold-water disease, intra-ovum infection, salmon