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NO52 - 4

Infectious Pancreatic Necrosis

Motohiko Sano*and Nobuaki Okamoto

Tokyo University of Marine Science and Technology, Tokyo 108-8477, Japan

ABSTRACT―Infectious pancreatic necrosis (IPN) was first reported in freshwater trout in 1940's in Canada and in 1950's in the USA, and subsequently spread around the world. The causative agent, infectious pancreatic necrosis virus (IPNV), which was the first fish-virus isolated in a cell culture, is a double-stranded RNA virus in the family Birnaviridae. In 1960's, Japanese rainbow trout aquaculture suffered a lot of fish losses at the fry stage, and the cause was confirmed to be IPNV by the virological study. In 1980's, IPN in Japan has gradually calmed down due to being worked synergistically with hatchery biosecurity practice, increase of host resistance and decrease of virus virulence. However, it is still one of the obstacles in the Atlantic salmon industry in the world.

Beko Disease of Cultured Fish in Japan

Hiroshi Yokoyama*

The University of Tokyo, Bunkyo, Yayoi 1-1-1, Tokyo 113-8657, Japan

ABSTRACT―Beko disease is derived from the concave body surface of fish infected with microsporidians in the myocytes. In this paper, several fish microsporidians including Microsporidium seriolae from Seriola spp. (S. quinqueradiata, S. dumerili and S. lalandi ), Microsporidium spp. from three other cultured fish, and Heterosporis anguillarum from Japanese eel Anguilla japonica are reviewed. A shift of eel-farming method from open field ponds to house-type heating culture systems has emerged the beko disease in cultured Japanese eel. Considering the successful transmission of H. anguillarum to uninfected juveniles, frequent screening in eel size seems to reduce the incidence of the disease in eel farms. Previously, beko disease of yellowtail S. quinqueradiata was not been considered as a serious problem, because yellowtail juveniles infected with M. seriolae usually recover from the disease until the time of adult stage. However, serious condition of the disease in cultured yellowtail has recently received attention as a re-emerging disease. Unknown life-cycle of M. seriolae makes the control measures difficult. As diagnostic methods, microscopic examination with Uvitex 2B staining and molecular tools with PCR have been developed. Furthermore, other related microsporidians have been reported in cultured red sea bream Pagrus major, hatchery-bred spotted halibut Verasper variegatus and juvenile Pacific bluefin tuna Thunnus orientalis.

Skin Fluke Infection of Cultured Marine Fish

Kazuo Ogawa1*and Sho Shirakashi2

1Meguro Parasitological Museum, Tokyo 153-0064, Japan
2Aquaculture Research Institute, Kindai University, Wakayama 649-2211, Japan

ABSTRACT―Capsalid monogeneans infect the skin of marine fish; among them, Benedenia seriolae and Neobenedenia girellae are most important pathogens of cultured fish. The former infects the skin of amberjacks, Seriola spp., while the latter, being not host specific, has been found from the skin of 15 fishes in Japan. Feeding epithelial cells and mucous of the host results in skin abrasion, causing growth retardation and secondary bacterial infection, even leading to the death of the host fish. Eggs entangle on the culture net, which is prone to heavy infection of fish cultured in net cages. Prevention of infection is practically impossible as its life cycle has been established in fish farms. Chemotherapy with hydrogen peroxide or praziquantel is effective but repeated treatment is required, as immunity is not acquired by infected fish. Development of new control measures such as biological control and selective breeding of a resistant strain against these monogeneans are in progress.

Blood Fluke Infection of Japanese Amberjack
Seriola quinqueradiata in Fish Farms along the Western
Coastal Area of Bungo Channel, Japan

Yutaka Fukuda1, Kazuyoshi Miyamura2, Etsuhisa Hitaka3, Keisuke Kimoto1,
Yasuhiro Sanada4,Takayuki Asai3and Kazuo Ogawa5*

1Fisheries Research Division, Oita Prefectural Agriculture, Forestry and Fisheries
Research Center, Oita 879-2602, Japan
2Fisheries Management Division, Agriculture, Forestry and Fisheries Department,Oita Prefectural Government, Oita 870-8501, Japan
3Oita Prefecture Southern Region Bureau, Oita 876-0813, Japan
4Oita Prefecture Central Region Bureau, Oita 870-0021, Japan
5Meguro Parasitological Museum, Tokyo 153-0064, Japan

ABSTRACT―Blood fluke infection among diseased Japanese amberjack Seriola quinqueradiata (n = 9,470) cultured in Oita Prefecture was monitored from 1992 to 2001. Infection was confirmed by the presence of parasite eggs accumulated in the gills. Amberjack with parasite eggs were found in all culture areas except for Usuki Bay. Eggs in the gills of 0-year-old fish started to be observed from early July, with the minimum body weight (BW) of 130 g in Yonouzu Bay, whereas in Nyuzu Bay egg-positive fish was first found in late August with the minimum BW of 296 g. Amberjack were cultured in the inner part of Nyuzu Bay up to the size of 200-250 g in BW, suggesting that infection occurred when fish were later moved to the mouth of the bay for further growth. In the inner part of Nyuzu Bay, hypoxia and conspicuously high dissolved inorganic nitrogen in the water near the bottom and acid volatile sulfides in the sediment were recorded every summer in the present survey. It is speculated that such extraordinary environment is unfavorable for the propagation of the intermediate host of the causative organism in the inner part, but not at the mouth, of the bay.

Key words: Seriola quinqueradiata, Japanese amberjack, blood fluke, distribution, environmental factor, Bungo Channel

Bactericidal Effects of Disinfectants on Yersinia ruckeri

Masatoshi Yamasaki1*, Takamitsu Sakai1, Takafumi Ito1 and Koh-ichiro Mori2

1Tamaki Laboratory, Research Center for Fish Disease, National Research Institute of Aquaculture,
Japan Fisheries Research and Education Agency, Mie 519-0423, Japan
2Research Center for Fish Disease, National Research Institute of Aquaculture,
Japan Fisheries Research and Education Agency, Mie 516-0193, Japan

ABSTRACT―Enteric redmouth disease caused by Yersinia ruckeri, is one of the most important aquaculture diseases worldwide. In this study, the effects of 11 disinfectants on Y. ruckeri ATCC29473 (2.8 × 108 CFU/mL) and Y. ruckeri FPC1215 (2.9 × 108 CFU/mL), were examined at 20°C. Nine disinfectants exhibited minimum bactericidal concentrations against both strains after 30 s exposure: 40% ethanol, 30% isopropanol, 4 mg/L povidone iodine, 1.25 mg/L sodium hypochlorite, 1:15,000 Rontect®, 1:3,840 Acecide®, 1:100 Hibiten®, 1:1,000 Osuban® and 1:1,000 Hyamine®. However, no disinfection effects were observed for Saponated cresol solution® or Pyceze®.

Key words: enteric redmouth disease, Yersinia ruckeri, disinfection, phenol coefficient

Survey on Perkinsus Species in Manila Clam Ruditapes philippinarum in Korean Waters Using Species-Specific PCR

Hyun-Sil Kang1, Hyun-Sung Yang2, Kimberly S. Reece3, Young-Ghan Cho1, Hye-Mi Lee1, Chul-Won Kim4 and Kwang-Sik Choi1*

1School of Marine Biomedical Science (BK21 PLUS), Jeju National University, Jeju 63243, Republic of Korea
2Jeju International Marine Science Center for Research and Education,
Korea Institute of Ocean Science & Technology (KIOST), Jeju 63349,
Republic of Korea
3Virginia Institute of Marine Science, College of William and Mary, Virginia 23062-1346, U.S.A.
4Korea National College of Agriculture and Fisheries, Jeollabuk-do 54874, Republic of Korea

ABSTRACT―We investigated possible infection with Perkinsus olseni and/or P. honshuensis in Manila clams in Korean waters using Perkinsus species-specific PCR. Ray's fluid thioglycollate medium assay revealed that 97.3% of the clams examined were infected with Perkinsus sp., with the mean intensity ranging from 2.2 × 104 to 6.8 × 106 cells/g gill. In the Perkinsus species-specific PCR assay, all the amplified Perkinsus-positive bands were identified as P. olseni, while none of P. honshuensis-specific band was amplified. Our survey results indicate that P. olseni is the main causative agent of perkinsosis in Manila clam populations in Korean waters, while more extensive survey must be carried out.

Key words: Perkinsus olseni, Perkinsus honshuensis, Ruditapes philippinarum, Perkinsus species-specific PCR, Korea

Red Sea Bream Iridoviral Disease in Hatchery-Reared
Devil Stinger Inimicus japonicus

Yasuhiko Kawato1*, Ikunari Kiryu1, Yoshihiro Kawamura2 and Kazuhiro Nakajima3

1Diagnosis and Training Center for Fish Diseases, National Research Institute of Aquaculture,
Japan Fisheries Research and Education Agency, Mie 516-0193, Japan
2North-Agricultural Technology Center, Hyogo Prefectural Technology Center for Agriculture,
Forestry and Fisheries, Hyogo 669-5254, Japan
3Project Management Department, National Research Institute of Fisheries and Environment of Inland Sea,
Japan Fisheries Research and Education Agency, Hiroshima 739-0452, Japan

ABSTRACT―A disease outbreak occurred in hatchery-reared devil stinger Inimicus japonicus (approximately 2 g). Abnormally enlarged cells specific for red sea bream iridoviral disease (RSIVD) were observed in the moribund fish. Red sea bream iridovirus (RSIV) genome (106.1-8.9 copies/mg tissue) were detected from the dead fish. The nucleotide sequence of the MCP gene of the isolated virus was identical to those of the RSIV isolates previously reported in Japan. In an infection trial, all of devil stinger intraperitoneally inoculated with the virus (102.3 TCID50/fish) died and the viral genome was detected from the dead fish at 106.9-9.2 copies/mg tissue. This is the first report of RSIVD in devil stinger.

Key words: red sea bream iridoviral disease, RSIVD, Inimicus japonicus, devil stinger, hatchery

Immunization of Rock Bream Oplegnathus fasciatus at Low Temperature by Immersion with Live Red Sea Bream Iridovirus (RSIV)

So-Young Oh, Hyun Jung Gye, Myung-Joo Oh and Toyohiko Nishizawa*

Department of Aqualife Medicine, Chonnam National University, Yeosu 59626, Republic of Korea

ABSTRACT―Rock bream Oplegnathus fasciatus were immersed in cultured RSIV suspension at 17°C for 30 min, and reared for 80 days without controlling temperature. Fish rearing temperature naturally increased at approximately 0.1°C/day from 17°C. Mortalities of fish without and with RSIV at 105.8, 103.8 and 101.8 TCID50/mL were 5.8%, 30.8%, 22.5% and 6.7%, respectively. Surviving fish were reared at 26°C, and intramuscularly injected with RSIV at 101.8 or 100.8 TCID50/fish. Survivors from RSIV-immersion at ≥ 103.8 TCID50/mL were strongly protected against RSIV challenge whereas those at ≤ 101.8 TCID50/mL died, suggesting that fish immunization with live RSIV at low temperature could be conducted by immersion route.

Key words: Megalocytivirus, red sea bream iridovirus, immunization, immersion, Oplegnathus fasciatus