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NO36 - 1 (2001)

Prophylactic Effects of Chemicals and Immunostimulants in Experimental Tetrahymena Infections of Guppy

August 17, 2000<>Aranya Ponpornpisit1, Makoto Endo2* and Hisashi Murata3<>1 United Graduate School of Agricultural Sciences, Kagoshima University, Kourimoto 1-21-24, Kagoshima 890-0065, Japan
2 Laboratory of Fish Pathology, Faculty of Agriculture, Miyazaki University, 1-1 Gakuen Kibanadai Nishi, Miyazaki 889-2192, Japan
3 Laboratory of Aquaculture, Faculty of Agriculture, Miyazaki University, 1-1 Gakuen Kibanadai Nishi, Miyazaki 889-2192, Japan

ABSTRACT ・The prophylactic effects of chemicals and immunostimulants on the Tetrahymena infection of guppies (Poecilia reticulata) were studied through experimental infections. Tetrahymena pyriformis was used in an experimental infection on a guppy population pre-treated by the following method; the base of the caudal fin was covered with a 10% acetic acid-soaked cotton strip for 3 min. The study consisted of screening anti-Tetrahymena chemicals, testing prophylactic effects of selected chemicals or immunostimulants, and finally evaluating the combination effects of the chemicals and immunostimulants. The single uses of chemicals or immunostimulants did not completely prevent the Tetrahymena infection. Prevention was attained by the combination of a 0.5% sodium chloride bath and a feeding of C-UPIII (a Chinese herb mix) diet.

Detection of Flavobacterium psychrophilum in Various Organs of Ayu Plecoglossus altivelis by in situ Hybridization

October 27, 2000<>Hong Liu?ェ Shotaro Izumi and Hisatsugu Wakabayashi*<>Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo 113-8657, Japan

ABSTRACT輸n in situ hybridization (ISH) using digoxigenin-labeled 16S rDNA probes was developed to detect the causative agent of bacterial coldwater disease, Flavobacterium psychrophilum. Strong, specific hybridization was observed for all F. psychrophilum strains tested and no cross-hybridization was seen for 13 other bacterial species. Distribution of F. psychrophilum in various organs of experimentally and naturally infected ayu was investigated by the ISH. A group of the experimental fish were given a sting at the skin and then immersed in a suspension of F. psychrophilum (106 CFU/mL) for 1 h at 15℃ and another group were subcutaneously injected with F. psychrophilum at a dose of 1.5※107 CFU/fish. In both experiments, F. psychrophilum was detected in the muscle, gills, heart, kidney and spleen, but not in the brain, liver, stomach, intestine, or pyloric caeca during the experiment period (7 h). A large number of F. psychrophilum were found at the stung or injected sites of the muscle, while no bacteria were detected at the intact muscle. In some of naturally infected ayu collected in fish farms, F. psychrophilum was detected in the liver, pancreas, stomach, pyloric caeca and intestine.

Anemia caused by Challenges with the Monogenean Neoheterobothrium hirame in the Japanese Flounder

November 14, 2000<>Tomoyoshi Yoshinaga1*, Takashi Kamaishi1, Isao Segawa1, Keisuke Yamano1 , Hanako Ikeda2 and Minoru Sorimachi3<>1 Inland Station, National Research Institute of Aquaculture, Tamaki, Mie 519-0423, Japan
2 Fukui Prefectural Fisheries Experimental Station, Tsuruga, Fukui 914-0843, Japan
3 National Research Institute of Aquaculture, Nansei, Mie 519-0193, Japan

ABSTRACT佑hallenges of the Japanese flounder Paralichthys olivaceus with the monogenean Neoheterobothrium hirame were carried out to clarify the cause of the anemia, recently prevailing in the Japanese flounder in Japan. Hematological changes very similar to those previously reported in both wild and cultured anemic flounder were produced by the challenges with H. hirame. In the challenged flounder, the hemoglobin concentration decreased considerably and abnormal immature and mature erythrocytes having vacuolated or weakly stained cytoplasm, which characterize this anemia, appeared. The relationships among hemoglobin concentration, the ratio of immature erythrocytes and the above morphological changes in the blood smear of the challenged fish were very similar to those in the naturally affected anemic flounder. These hematological changes showed a clear correlation with the number of adult worms. These results, together with the previous findings, suggest that N. hirame is the main cause of the anemia prevailing in the Japanese flounder.

Microhabitats and Mode of Attachment of Neoheterobothrium hirame, a Monogenean Parasite of Japanese Flounder

December 18, 2000<>Hilal Anshary and Kazuo Ogawa*<>Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences,
The University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8657, Japan

ABSTRACT ・A survey of Neoheterobothrium hirame infection of Japanese flounder Paralichthys olivaceus in several places in Japan (Kyoto, Fukui and Ibaraki) was conducted to examine the relationship between the development of the parasite and its microhabitats. The parasite first attached to the gill filaments, then migrated to the gill arches/rakers and finally moved to the buccal cavity wall. This migration was associated with growth and maturity of the parasite. Some worms already reached maturity on the gill rakers, but produced eggs only on the buccal cavity wall. The histology of infected tissues was examined to determine the mode of attachment and pathological effects of the parasite. On the gill filaments, the parasite used, at first, marginal hooks and hamuli to attach to the proximal region of the secondary gill lamellae and later, clamps to grasp these lamellae. On the gill arches/rakers, clamps were used to attach to the epithelium. On the buccal cavity wall, clamps were used initially for attachment to the tissue surface but later the haptor penetrated the underlying connective and muscle tissues until the haptor and almost the entire isthmus region were embedded deeply in the host tissue. Only a mild inflammatory response was observed on the gill filaments and in the epithelium of the gill arches/rakers, respectively, whereas a strong host response and necrosis were associated with the prolonged attachment of the parasite to the buccal cavity wall.

A Study of Long-term Changes in Summer Infection Levels of Japanese Flounder Paralichthys olivaceus with the Monogenean Neoheterobothrium hirame in the Central Sea of Japan, with an Application of a New Technique for Collecting Small Parasites from the Gill Filaments

December 19, 2000<>Hilal Anshary1, Kazuo Ogawa1*, Masahito Higuchi2 and Tetsuo Fujii3<>1 Department of Aquatic Biosciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8657, Japan
2 Aquaculture and Biotechnology Division, Niigata Prefectural Fisheries and Marine Research Institute, Ikarashi, Niigata 950-2171, Japan
3 Japan Sea National Fisheries Research Institute, Suido-cho, Niigata 951-8121, Japan

ABSTRACT湧eoheterobothrium hirame infection of 0-year wild Japanese flounder Paralichthys olivaceus was investigated. This study was based on annual samples (preserved in formalin or alcohol) totalling 316 fish caught off Igarashi-hama in July and/or August of 1989・993 and 505 fish caught off Murakami City in August of 1993・999, Niigata Prefecture. A stirring method was developed to collect the monogenean from the fixed gill filaments. All the parasites were dislodged from the fixed gill filaments by stirring gills of individual hosts in 150 mL of water with a magnet (40 mm long and 8 mm in diameter) at 1150・200 rpm for 20 min and 30 min for the 0-year fish and 1-year fish, respectively. Adult parasites were macroscopically observed on the buccal cavity wall, whereas immature ones on the gill arches and rakers were detected under a stereomicroscope. No N. hirame was found from 1989 to 1992. The earliest records were from samples caught off Igarashi-hama and Murakami City in 1993, though the prevalence of infection was very low. The parasite occurrence changed annually in the Murakami samples. The annual fluctuations may have been influenced by the infection level of co-existing 1-year fish and the population size of 0-year fish recruited each year. It is inconclusive whether or not the monogenean is an indigenous parasite of Japanese flounder in this area.

Effect of low environmental temperature on embryonic development and egg hatching of Diplectanum aequans (Monogenea, Diplectanidae) infecting European sea bass, Dicentrarchus labrax

May 29, 2000<>Stefano Cecchini1*, Marco Saroglia1, Anna Maria Cognetti-Varriale2, Genciana Terova1 and Gabriella Sabino1<>1 Department of Sciences of Animal Production, Aquaculture Section, University of Basilicata, Via N. Sauro, 85100 Potenza, Italy
2 Department of Animal Pathology, University of Pisa, Viale delle Piagge 2, 56100 Pisa, Italy

ABSTRACT裕he effect of low incubation temperature on the embryonic development and larval hatching of the monogenean Diplectanum aequans, a gill parasite of sea bass Dicentrarchus labrax, was studied. Groups of eggs of D. aequans were incubated at 5℃ for different time periods (from 24 h to 28 days) before incubation at room temperature (18℃). Percentages of hatched larvae, aborted larvae and undeveloped embryos were estimated in comparison with the control group. Results show that eggs of the parasite are able to survive at 5℃, with a percentage that decreases as the incubation time at 5℃ increases, reducing the rate of larval hatching.

Pasteurellosis in Reared Hybrid Striped Bass (Morone saxatilis ラMorone chrysops)

August 14, 2000<>Hsu-Tien Huang1, Chien Tu2*, Sheng-Hsiung Chuang1, Hsin-Hsiung Hung1, Je-Fu Su2 and Shih-Yuh Lin2<>1 Pingtung Hsien Livestock Disease Control Center, Pingtung, Taiwan, ROC
2 National Institute for Animal Health, Tansui, Taiwan, ROC

ABSTRACT輸n outbreak of a disease occurred in
hybrid striped bass (20・5 cm in length) Morone saxatilis※Morone chrysops cultured in Taiwan. No significant external sign was found, whereas prominent nodules were observed in internal organs, such as the spleen and kidney. The most severe histopathological changes were necrotic foci and multiple granulomas in haematopoietic tissues of the spleen and kidney. The results of biochemical examination and PCR-based
detection indicate that the disease was caused by Photobacterium damselae subsp. piscicida. This is the first reported outbreak of pasteurelosis in cultured hybrid striped bass.

Susceptibility of fish cultured in subtropical area of Japan to red sea bream iridovirus

November 20, 2000<>Motohiko Sano1*, Megumi Minagawa1, Akihiro Sugiyama2 and Kazuhiro Nakajima3<>1 Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Ishigaki, Okinawa 907-0451, Japan
2 Okinawa Prefectural Fisheries Experimental Station, Itoman, Okinawa 901-0305, Japan
3 National Research Institute of Aquaculture, Nansei, Mie 516-0193, Japan

ABSTRACT祐usceptibilities of spangled emperor Lethrinus nebulosus, estuary cod Epinephelus malabaricus and cobia Rachycentron canadum cultured in subtropical Japan to red sea bream iridovirus (RSIV) were studied by experimental infections. Estuary cod showed as high susceptibility to RSIV as red sea bream Pagrus major. In contrast, the susceptibilities of spangled emperor and cobia to the virus were comparatively low. The result corresponds with the occurrence of the disease in the net cages.

Experimental Streptococcus iniae infection in Japanese flounder Paralichthys olivaceus

December 13, 2000<>Huu Thinh Nguyen, Kinya Kanai* and Kazuma Yoshikoshi<>Graduate School of Marine Science and Engineering, Nagasaki University,1-14 Bunkyo Machi, Nagasaki 852-8521, Japan

ABSTRACT裕he capability of Streptococcus iniae to cause disease in Japanese flounder was investigated by oral and bath (30 min) challenges with low, medium and high inoculation doses. Only with the highest inoculation dose, 9.9※107 CFU/100 g body weight, the oral challenge induced deaths. In the bath challenge deaths were induced even at the lowest inoculation dose, 2.9※103 CFU/mL water. Hemorrhagic lesions on the fins were observed in dead fish challenged by both methods. It is suspected that S. iniae entered through the body surface such as abrasive sites of the fins to cause disease.