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NO48 - 1 (2013)

Two Species of Cardicola (Trematoda: Aporocotylidae)
Found in Southern Bluefin Tuna Thunnus maccoyii
Ranched in South Australia

Sho Shirakashi1, Kazunobu Tsunemoto1, Claire Webber2, Kirsten Rough2, David Ellis2 and Kazuo Ogawa3*

1Fisheries Laboratory, Kinki University, Wakayama 649-2211, Japan
2Australian Southern Bluefin Tuna Industry Association, Port Lincoln SA 5606, Australia
3Meguro Parasitological Museum, Tokyo 153-0064, Japan
(Received December 21, 2012)

ABSTRACT―We determined the identity of an aporocotylid blood fluke discovered in the gills of southern bluefin tuna Thunnus maccoyii ranched in Australia. Both morphological and molecular data indicate the parasite is Cardicola orientalis, reported previously only from Pacific bluefin tuna T. orientalis in Japan. Over 70 C. orientalis adults were retrieved from a single gill arch of an infected southern bluefin tuna and numerous eggs were observed in the gill filaments suggesting possible pathology to the host. In addition, we obtained new information on morphological characteristics and molecular sequences of C. forsteri infecting the heart of T. maccoyii. This is the first report of C. orientalis in T. maccoyii, which may have a significant impact on the ranching industry of southern bluefin tuna and warrants further investigation.
Key words: blood fluke, Cardicola forsteri, Cardicola orientalis, tuna ranching, Thunnus maccoyii

Disinfection of Fertilized Grouper Eggs with Electrolyzed Seawater for Prevention of Viral Nervous Necrosis

Ken-ichi Watanabe1*, Kentaro Ide2, Takashi Iwasaki2, Jun Satoh2, Koh-ichro Mori2 and Tohru Mekata2

1Faculty of Bio-Industry, Tokyo University of Agriculture, Hokkaido 099-2493, Japan
2National Research Institute of Aquaculture, Fisheries Research Agency, Oita 879-2602, Japan
(Received August 30, 2012)

ABSTRACT―Conditions of fertilized egg disinfection with electrolyzed seawater were optimized to prevent vertical transmission of betanodavirus in longtooth grouper Epinephelus bruneus and sevenband grouper E. septemfasciatus. The treatments were performed by immersing eggs in electrolyzed seawater containing 0 to 1.5 mg/L of free chlorine. The conditions which showed no adverse effect on hatching rates of both species were 0.3 to 0.5 mg/L of free chlorine for 5 min, 1.0 mg/L for 3 min and 1.5 mg/L for 1 min. More than 99.4% of betanodavirus (SGNNV) was inactivated by the treatments of 0.3 to 1.0 mg/L of free chlorine for 3 min and 1.5 mg/L for 1 min.
Key words: Epinephelus bruneus, Epinephelus septemfasciatus, viral nervous necrosis, egg disinfection, electrolyzed seawater

A Probiotic Potential of Enterococcus gallinarum against Vibrio anguillarum Infection

Lita Sorroza, Fernando Real, Félix Acosta, Begoña Acosta, Soraya Déniz, Lorena Román, Fatima El Aamri and Daniel Padilla*

University Institute of Animal Health (IUSA), University of Las Palmas de Gran Canaria (ULPGC), Arucas 35416, Spain
(Received August 31, 2012)

ABSTRACT―The aim of this study was to look for new potential probiotic bacterial strains for marine aquaculture. Only one of 195 isolates from the gut of cultured fish including sea bass Dicentrarchus labrax, gilthead sea bream Sparus aurata, meagre Argyrosomus regius and sole Solea solea showed a strong inhibitory effect against Vibrio anguillarum. This isolate, identified as Enterococcus gallinarum, also produced a moderated protective effect against V. anguillarum infection of sea bass. Intraperitoneal injection with the isolate showed no pathogenicity in sea bass. Thus, the isolate designated E. gallinarum L1 can have a potential of probiotic bacterium.
Key words: Enterococcus gallinarum, inhibitory activity, Vibrio anguillarum, probiotic, Dicentrarchus labrax

Effects of Temperature and Salinity on the in vitro Proliferation of Trophozoites and the Development of Zoosporangia in Perkinsus olseni and P. honshuensis, Both Infecting Manila Clam

Kousuke Umeda, Jun Shimokawa and Tomoyoshi Yoshinaga*

Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
(Received October 9, 2012)

ABSTRACT―We evaluated the effects of temperature and salinity on in vitro trophozoite proliferation and zoosporangial development in Perkinsus olseni and P. honshuensis, infecting Manila clam. Trophozoite proliferation was highest at 28°C for both species and at 18-21‰ and 21-33‰ for P. olseni and P. honshuensis, respectively. Zoospore release rates, as the indicator of zoosporulation, were highest at 25-30°C and 25-35‰ for both species. However, these results seem not to explain the previously observed phenomena, i.e. lower infection prevalence in estuarine tidal flats (the two species not distinguished) and higher infection prevalence of P. olseni than P. honshuensis.
Key words: Perkinsus olseni, Perkinsus honshuensis, temperature, salinity, Ruditapes philippinarum

The Variation in Virulence among Flavobacterium psychrophilum Strains Isolated from Chum Salmon Oncorhynchus keta

Naoyuki Misaka1*, Makoto Hatakeyama2, Nobuhisa Koide2 and Kunio Suzuki3

1Head Office of Fisheries Institute, Hokkaido Research Organization, Hokkaido 046-8555, Japan
2Salmon and Freshwater Fisheries Institute, Hokkaido Research Organization, Hokkaido 061-1433, Japan
3Salmon and Freshwater Fisheries Institute, Donan Research Branch, Hokkaido Research Organization, Hokkaido 043-0402, Japan
(Received October 23, 2012)

ABSTRACT―We investigated virulence and elastin-degrading activity in ten strains of Flavobacterium psychrophilum isolated from chum salmon Oncorhynchus keta in Hokkaido, Japan through 2004 to 2006. Intraperitoneal injection of these strains to chum salmon fry revealed that 50% lethal doses (LD50) of the strains were from 2.6 × 105 to 4.7 × 107 CFU/g. No clear relationship between elastin-degrading activity and virulence in these strains was found. These results indicate that the virulence of F. psychrophilum isolated from chum salmon varies considerably among strains, and is not clearly related to elastin-degrading activity.
Key words: Flavobacterium psychrophilum, LD50, virulence, elastase, Oncorhynchus keta, chum salmon

Optimizing the Quantitative Detection of Red Seabream Iridovirus (RSIV) Genome from Splenic Tissues of Rock Bream Oplegnathus fasciatus using a qPCR Assay

So-Young Oh and Toyohiko Nishizawa*

Department of Aqualife Medicine, Chonnam National University, Yeosu 550-749, Korea
(Received November 2, 2012)

ABSTRACT―We optimized the quantitative detection of red seabream iridovirus (RSIV) genome from splenic tissues of rock bream Oplegnathus fasciatus using the quantitative polymerase chain reaction assay targeting the Pst I fragment gene. The regression line for quantitative detection of the RSIV genome was y = -0.266x + 10.95 (amplification efficacy: 84.5%), which was available between Ct 8 and 33. The quantitative-detection limit of the assay was 103.5 genomes/mg. The RSIV genome was under the quantitative-detection limit in fish by day 7 of RSIV inoculation, whereas ≥ 106.71±1.77 genomes/mg (mean ± SD) of RSIV were detected in fish from 10 days after RSIV inoculation.
Key words: red seabream iridovirus, RSIV, megalocytivirus, Oplegnathus fasciatus, qPCR

Shading Reduces Neobenedenia girellae Infection on Cultured Greater Amberjack Seriola dumerili

Sho Shirakashi1*, Chihaya Hirano1, Asmahani binti Asmara2, Noorashikin binti Md Noor2, Katsuya Ishimaru1 and Shigeru Miyashita1

1Fisheries Laboratory, Kinki University, Wakayama 649-2211, Japan
2Borneo Marine Research Institute, University of Malaysia Sabah, Kota Kinabalu 88400, Malaysia
(Received November 7, 2012)

ABSTRACT―Juvenile greater amberjack were placed in a small cage and exposed to Neobenedenia girellae oncomiracidia for 48 h at an amberjack culture site under natural light or with a shade. The shading reduced worm intensity on the skin of fish by about 70%. Additional laboratory experimental infection comparing the larval infectivity under dark and light conditions revealed that the oncomiracidia were capable of infecting fish in complete darkness. These results suggest that the low infection rate in the shaded water is probably due to accumulation of the oncomiracidia into the bright area, resulting in the lowered density under the shade.
Key words: skin fluke, Monogenea, light intensity, Neobenedenia girellae, Seriola dumerili

Protective Efficacy of a Commercial β-hemolytic Streptococcus Vaccine for Japanese Flounder against Streptococcus iniae Infection of Threadsail Filefish

Yuji Ishii1, Toshiyuki Yamada2, Yukitaka Sugihara2, Ikuo Takami3, Koushirou Suga1 and Kinya Kanai1*

1Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Nagasaki 852-8521, Japan
2Nagasaki Prefectural Institute of Fisheries, Nagasaki 851-2213, Japan
3Tsushima Fisheries Expansion Advisory Center, Nagasaki 817-0324, Japan
(Received December 27, 2012)

ABSTRACT―A commercial β-hemolytic Streptococcus vaccine for Japanese flounder was examined for the protective efficacy against Streptococcus iniae infection of threadsail filefish Stephanolepis cirrhifer. In the artificial infection test a high mortality rate (90%) was obtained by intramuscular inoculation with S. iniae as low as 102 CFU/100 g body weight. In the vaccination test intraperitoneal inoculation with the vaccine at the usual and 1/10 dosages resulted in a high protective effect (RPS≧85%), and the high protective efficacy was kept for at least 7 months.
Key words: Stephanolepis cirrhifer, threadsail filefish, Streptococcus iniae, vaccine, efficacy