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NO48 - 3

The Occurrence of Caligus sclerotinosus (Caligidae) Infection in Cultured Red Sea Bream Pagrus major and Involvement of Phototaxis in Fish-to-fish Transfer of the Adults

Shinji Tanaka1*, Shinji Yamamoto2 and Kazuo Ogawa3
1Mie Prefecture Fisheries Research Institute, Mie 517-0404, Japan
2Nanto Nursery Center, Minami-ise Town Fisheries Nursery Institute, Mie 516-1306, Japan
3Meguro Parasitological Museum, Tokyo 153-0064, Japan

(Received December 11, 2012)

ABSTRACT―The occurrences of Caligus sclerotinosus, a parasitic copepod on cultured red sea bream Pagrus major, were surveyed in fish farms and the phototaxis of adult caligid was experimentally examined. The parasite infection occurred from April to December, in which up to approximately 500 caligids infected the external surface of each diseased fish, covering the whole body surface, eyes and fins. The main disease signs were scale exfoliation, abrasion and ulcerative lesions on the body surface, and chipped fins. Listless swimming near the water surface was also observed. Daily mortalities were usually below 0.1%. When illuminated at different light intensities, most adult caligids showed positive phototaxis and those illuminated at 50 mmol/m2/s swam significantly faster than those illuminated at 200 and 800 mmol/m2/s. When infected fish were illuminated from one direction in a tank, 2.5% of caligids moved from fish to the illuminated wall of tank. When an infected fish and an uninfected fish were separated with a screen partition in each tank and illuminated from one side, 25% of caligids moved from fish in the shaded side to fish in the illuminated side, but never vice versa, showing that fish-to-fish transfer of C. sclerotinosus adults was affected by light conditions.
Key words: Caligus sclerotinosus, Pagrus major, phototaxis, fish-to-fish transfer, occurrence, behavior

Pathogenicity of Streptococcus iniae and Lactococcus garvieae in Farmed Thread-sail Filefish and Efficacy of the Formalin-killed Vaccines against These Bacteria

Takayuki Minami1*, Masanori Kanemaru1, Kazuo Iwata1, Masakazu Kuwahara2, Kenichi Amano2, Atushi Mizuta3, Nobuhiro Maeda4, Issei Nishiki5, Yuya Tue5 and Terutoyo Yoshida5
1Miyazaki Prefectural Fisheries Research Institute, Miyazaki 889-2162, Japan
2Matsuoka Research Institute for Science, Tokyo 184-0003, Japan
3Miyazaki Prefectural Fisheries Promotion Association, Miyazaki 819-0322, Japan
4Miyazaki Prefectural Miyazaki Marine High School, Miyazaki 880-0856, Japan
5Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan

(Received March 19, 2013)

ABSTRACT―The virulence of Streptococcus iniae and Lactococcus garvieae strains was evaluated in farmed thread-sail filefish Stephanolepis cirrhifer by intraperitoneally injecting live bacterial cells. These two pathogens were highly pathogenic to thread-sail filefish. The efficacy of each commercial vaccine, namely, S. iniae vaccine, L. garvieae vaccine, and a combined vaccine of S. iniae and L. garviae was evaluated in the fish. The mortality was significantly lowered in both S. iniae- and L. garvieae-vaccinated groups compared to the control group, and both vaccines showed strong protection against the respective pathogens. Moreover, the combined vaccine showed strong protection against these two pathogens. These results suggest that these commercial vaccines are applicable in filefish aquaculture.
Key words: Stephanolepis cirrhifer, Streptococcus iniae, Lactococcus garvieae, thread-sail filefish, streptococcosis, pathogenicity, aquaculture, vaccine

Occurrence of the Myxosporean Emaciation Disease Caused by Enteromyxum leei in Cultured Malabar Grouper Epinephelus malabaricus

Machiko China1, Hiroyuki Nakamura2, Kaoru Hamakawa3, Eishin Tamaki2, Satoshi Miwa4, Fei Meng5† and Hiroshi Yokoyama5*

1Yaeyama Agriculture, Forestry and Fisheries Promotion Center, Okinawa 907-0002, Japan
2Okinawa Prefectural Sea Farming Center, Okinawa 905-0212, Japan
3Okinawa Prefectural Fisheries Research and Extension Center, Okinawa 901-0305, Japan
4National Research Institute of Aquaculture, Fisheries Research Agency, Mie 519-0423, Japan
5Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan

(Received May 29, 2013)

ABSTRACT―In 2008, the myxosporean emaciation disease was found in cultured Malabar grouper Epinephelus malabaricus in a fish farm in Okinawa Prefecture, Japan. The disease occurred in winter when water temperature ranged from 21 to 26°C, and the cumulative mortality reached 20-50% among culture tanks. In affected fish, cranial bones were externally apparent due to severe emaciation. The intestinal wall was very thin and the liver exhibited conspicuous green color. Morphological and molecular analyses demonstrated that the causative myxosporean was Enteromyxum leei. Histopathological examinations revealed that the epithelia of the intestine and bile duct of diseased fish were heavily infected with E. leei. The common bile duct was often obstructed by severe inflammation with degenerated tissues and bacteria, suggesting that the abnormal color of the liver was caused by cholestasis. Some diseased fish recovered in a laboratory when water temperature increased naturally to 27-30°C in summer months, and the parasite was not detected in those fish. Experimental transmission of E. leei to naïve Malabar grouper was successfully achieved by cohabitation with infected grouper or by feeding with the feces of infected fish. This is a new host and locality record for E. leei.

Key words: Enteromyxum leei, myxosporean emaciation disease, Epinephelus malabaricus, Malabar grouper, Myxozoa

Low Possibility of Intra-Ovum Infection with Flavobacterium psychrophilum or Renibacterium salmoninarum in the Salmonid Coelomic Cavity

Masakazu Kohara1*, Hisae Kasai2 and Mamoru Yoshimizu2

1Nagano Prefectural Fisheries Experimental Station Saku-branch, Nagano 385-0042, Japan
2Faculty of Fisheries Sciences, Hokkaido University, Hokkaido 041-8611, Japan

(Received January 29, 2013)

ABSTRACT―In this study, rainbow trout Oncorhynchus mykiss and amago salmon O. masou were used to study intra-ovum infection with Flavobacterium psychrophilum and Renibacterium salmoninarum, respectively. To investigate the possibility of intra-ovum infection of eggs in the coelomic cavity, the contamination of coelomic fluid and egg contents from ripe females were examined. The ranges of viable counts of F. psychrophilum and R. salmoninarum in coelomic fluid were 101.0-4.2 and 101.6-9.9 CFU/mL, respectively. However, neither F. psychrophilum nor R. salmoninarum was isolated from the egg contents. It was concluded that there was little possibility of intra-ovum infection of salmonid eggs in the coelomic cavity.
Key words: intra-ovum infection, coelomic fluid, salmonid egg, Flavobacterium psychrophilum, Renibacterium salmoninarum

Detection and Genetic Characterization of Lymphocystis Disease Virus (LCDV) Isolated during Disease Outbreaks in Cultured Gilt-head Sea Bream Sparus aurata in Tunisia

Sondès Haddad-Boubaker1*, Nadia Bouzgarou2, Emna Fakhfakh1, Monia Khayech2, Souhail Ben Mohamed2, Aida Megdich1 and Noureddine Ben Chéhida1

1Laboratory of Virology, Veterinary Research Institute of Tunisia, Tunis 1006, Tunisia
2Regional Center of Veterinary Research of Sousse, Sousse 4000, Tunisia

(Received February 1, 2013)

ABSTRACT―Lymphocystis disease virus (LCDV) causes a self-limiting disease in fish. However, recently, LCD outbreaks have increased, causing significant mortalities. In this study, we report the occurrence of two disease outbreaks in reared gilt-head sea bream Sparus aurata in the Tunisian coast. Presence of LCDV in diseased fish was confirmed by virus isolation using BF-2 cells and PCR amplification targeting the polymerase gene. Amino acid sequence analysis of the major capsid protein suggested that the LCDV strain was identical to nine strains previously isolated from the Mediterranean, Red Sea and South Atlantic coasts of Europe. These strains might have been disseminated through recent international trade.
Key words: Sprarus aurata, lymphocystis disease virus, phylogeny, aquaculture, Tunisia

Mortality of Cultured Ayu Plecoglossus altivelis with Deep Skin Ulceration on the Thoracic Region

Takashi Okamura
Shiga Prefectural Fishery Experiment Station, Shiga 522-0057, Japan

(Received March 21, 2013)

ABSTRACT―An episode of mortality was observed in cultured ayu Plecoglossus altivelis with clinical signs including deep ulceration in the thoracic skin in affected fish in the Shiga Prefecture, Japan, in June, 2012. Bacteriological examination revealed that fish were infected with Flavobacterium psychrophilum, the etiologic agent of bacterial cold water disease (BCWD). Deep thoracic ulceration has not been reported in cases of BCWD in ayu. This lesion was successfully reproduced in ayu by slightly abrading the skin in the thoracic region prior to immersion challenge with F. psychrophilum. However, I could not determine the causative factor of the lesion in conventional fish farm management.
Key words: Plecoglossus altivelis, ayu, bacterial cold water disease, deep ulceration, Flavobacterium psychrophilum