Tokuo Sano

Principal microbial diseases of mariculture in Japan

Abstract The most important microbial diseases encountered in the rapidly developing mariculture industry of Japan are described. Vibriosis, pseudotuberculosis, streptococcicosis, nocardiosis and bacterial kidney disease (BKD) were the most important bacterial infections, resulting insignificant losses in mariculture fish production. Viral infections with epizootic outbreaks were observed with yellowtail fry and Japanese flounder. In kuruma shrimp culture, problems were caused by vibriosis and a Baculovirus sp. The annual damage and losses due to diseases in mariculture in Japan in 1984 are tabulated. An overview is given of the drugs allowed and used for treatment of diseases of marine fish in Japan.

Resistance of a rainbow trout strain to infectious pancreatic necrosis

Infectious pancreatic necrosis (IPN) is a well-known acute viral disease of hatchery-reared salmonid fishes, but so far no effective treatment for IPN has been developed. This report is of a strain (RT-201) of rainbow trout resistant to IPN. The strain, which evolved in a commercial hatchery, was artificially challenged with IPN virus at 15°C for 28 days. The population was tested totally 20 times throughout 1979–1989 and the average (±standard deviation) mortality was 4.3±5.7% whereas in the positive controls (RT-101 strain, highly sensitive to IPN) it was 96.1±5.5%. In the 5th generation of an isolate of RT-210 reared at a public station without any pathogens there was 5.0% mortality and in the positive control (RT-101) it was 100%. The differences in mortality between the RT-201 and the RT-101 (positive control) were significantly different (P<0.005). Distribution of female families of the population with various levels of mortality to an IPNV challenge was 7.6±7.4% (n=22, range 0–23%). The results indicate that the resistance manifested in strain RT-201 was genetically transmittable and relatively stable. This interesting evidence underscores the importance of a genetic link-up of pathological investigations.

ISOLATION AND CHARACTERIZATION OF A NEW HERPESVIRUS FROM EEL

ABSTRACT: A new virus was isolated from both the Japanese eel ( Anguilla japonica ) and the European eel ( A. anguilla ) cultivated in an intensive culture system in Japan. The virus grew less well in BF-2, CEA, FHM, CHH-1, RTG-2 than in eel cell lines (EK-1, EO-2). It could not grow in amphibian and mammalian cell lines. The cytopathic effect observed in an eel kidney (EK-1) cell line consisted of typical syncytium formation and rounded cells in which Cowdry type A intranuclear inclusions were observed. The optimal growth temperature was 20–25°C. This virus differed serologically from Ictalurid herpesvirus 1 (Channel catfish virus; CCV), Salmonid herpesvirus 2 (Nerka virus of Towada lake, Akita, and Aomori; NeVTA), and Cyprinid herpesvirus 1 ( Herpesvirus cyprini; CHV). There were 25 virion polypeptides found in this virus, ranging from 19.5K to 320K as determined by SDS-polyacrylamide gel electrophoresis. Viral DNA, whose molecular weight was calculated to be about 100 × 10 6 , was infectious. We have designated this virus as Anguillid herpesvirus 1, with Herpesvirus anguillae as the latinized name and Eel herpesvirus as the vernacular name.

Baculoviral mid-gut gland necrosis (BMN) of kuruma shrimp(Penaeus japonicus) larvae in Japanese intensive culture systems

In many shrimp farms in the Kyushu and Chugoku areas of Japan, the so-called mid-gut gland cloudy disease of kuruma shrimp larvae(Penaeus japonicus) has occurred since 1971. The pathological changes associated with this baculoviral mid-gut gland necrosis (BMN) are extensive cellular necrosis, collapse of mid-gut gland cells, nuclear hypertrophy and finally karyorrhexis. Electron microscopic examination revealed the presence of virions and virogenic stages in the affected nuclei. Average length and diameter of the virions detected was 310 and 72 nm, respectively; nucleocapsids were 250 nm in size. Virions enclosing 2 nucleocapsids within a single envelope were rarely found. The spirally arranged capsomeres were at an angle of 37 to 38° to a horizontal line meeting at right angles with the long axis of the virion. Infectivity trials resulted in high mortality of healthy mysis and juveniles (2nd post-larval stage). Juveniles at the 9th post-larval stage showed no mortality, although they could be infected easily by the agent. Hypertrophied nuclei in squashed and stained preparations of the affected gland cells can be considered to be of reliable presumptive diagnostic character, and fluorescent antibody staining can be employed to confirm the diagnosis of BMN.

Viruses and viral diseases of salmonids

Abstract Salmonid fishes are one of the most important aquatic resources in the world, and since salmonid fish culture was initiated many years ago, it has been developing with the times in several countries. In particular, the intensive culture of rainbow trout, Oncorhynchus mykiss, has developed over the past 30 years in the USA, Europe, Japan and elsewhere. However, the successes achieved have brought with them diverse new disease problems for rainbow trout and other salmonids. The crucial problems are communicable or infectious diseases caused by bacterial and viral agents, among which viral disease is the most serious, because diagnosis is difficult, the majority of the epizootics is acute or subacute, and furthermore, no chemotherapy is available for them. The viral agents, the viral infections and the pathologic conditions of salmonid fishes can be grouped into the respective viral families according to the attributes of the virus, and into an unclassified virus group as follows. RNA VIRUS GROUP: Birnaviridae, Paramyxoviridae, Picornaviridae, Reoviridae (Reovirus and Rotavirus), Retroviridae, Rhabdoviridae, and Togaviridae: DNA VIRUS GROUP: Adenoviridae, Herpesviridae and Iridoviridae. In addition to the viral diseases which have been internationally recognised, this review gives new information on other diseases including Salmonid Picornalike Viruses, Landlocked Salmon Virus (LSV), Atlantic Salmon Rotavirus (ASR), Trout Strawberry Disease (TSD), Coho Salmon Tumor Virus (CSTV), Epizootic Epitheliotropic Disease of Lake Trout, Epizootic Hematopoietic Necrosis (EHN) of Trout, Erythrocytic Inclusion Body Syndrome (EIBS). Intraerythrocytic Viruslike Particles different from EIBS in Atlantic Salmon, and Third Erythrocytic Virus associated with anemia. Among these, the pathologic conditions from which a causative virus has been isolated are Coho Salmon Tumor, Epizootic Hematopoietic Necrosis of Trout, Trout Strawberry Disease, Atlantic Salmon Rotavirus Disease, and Landlocked Salmon Virus Disease. Furthermore, Salmonid Picornalike Virus and Cutthroat Trout Virus have been isolated from the asymptomatic condition. The rest are viral infections with the viruses visualized but not yet isolated. This article deals with over twenty viruses, viral diseases and pathologic conditions of salmonids.

A novel tissue organized in the primary hemolymph culture of Penaeus japonicus Bate

Hemolymph from an outwardly healthy kuruma shrimp, Penaeus japonicus Bate, drawn into a syringe with anticoagulant was incubated in a culture flask containing Naga-Sas medium at 20°C. The pleomorphic cells which showed vigorous growth formed multilayers of the primary hemolymph culture via formation of a primary matrix within 40 h after incubation. In vitro organogenesis was recognized after 21 days. The in vitro tissue, secondary matrix (SM), was designated as in vitro penaeid hematopoietic tissue. The SM produced suspending prohyalocyte complexes and static prohyalocytes. The mechanically separated SM pieces were cultured, and slowly grew to SM of visible size via diverse and pleomorphic organism which produced prohyalocytes; a developmental continuity was recognized between prohyalocytes and SM. In vitro prohyalocytes never developed to hemocytes. The diverse organisms which SM produced had originated from prohyalocytes of the animal, but those organisms were nonexistent in the circulating hemolymph.

Immunogenic effect of attenuated IHNV clones, AF71-1 and AF71-1CL3, in rainbow trout and kokanee.

The immunogenic activities of attenuated IHNV clones, AF71-1 and AF71-1-CL3, were examined in this study. These two clones had been purified from successively subcultured IHNV by plaquing, subsequently selected through infectivity trials. Rainbow trout and/or kokanee were immunized with the two IHNV clones by intraperitoneal (IP) injection or water-born method, subsequently challenged with virulent IHNVs. By IP injection, the immunization with AF71-1 was extremely effective in rainbow trout and kokanee, but less or no effect by water-born immunization. The immunogenic activity of AF71-1•CL3, which had been clone purified from AF71-1 by limiting dilution method, was determined in rainbow trout and almost the same results as AF71-1 were obtained. Remarkable protective effect was achieved in AF71-1•CL3 immunized fish by IP injection at the amount of 102.0TCID50/fish.

Comparison between EPC and FHM cell lines on IHN virus susceptivility and effect of fetal bovine serum concentration on IHNV-CPE appearance

牛胎児血清濃度を1,2,5％としたMEMでEPCとFHM細胞をマイクロプレートに調整し, IHNV長野分離株のウイルス力価を測定したところ, 高い血清濃度はCPEの発現を遅らせ, 力価を緩慢に上昇させ, 最終力価に達するまでにより長期間を要した。最終力価では血清濃度による明瞭な差は生じなかった。FHM細胞ではCPEぼ発現も遅く, MEM-2で調整した両細胞により多数の試料を測定して比較したところ, IHNV長野分離株に対し, FHM細胞はEPC細胞よりも明らかに低感受性であった。