Mortality associated with edema occurred in juvenile Japanese char Salvelinus leucomaenis. Scanning electron microscopy of gill surfaces and histological observations of the gills and kidneys of diseased juveniles indicated that the present pathological changes of the edema disease in juvenile Japanese char (EJJC) were similar to those of the previous study. We conducted three experiments to investigate curative and preventive measures for EJJC: a bath treatment with 1.0% salt water for a curative effect in the early stage of the disease, supplementation of ascorbic acid to the commercial diet (10,000 mg/kg diet) for prevention of the disease, and the supplementation of ascorbic acid along with increased water flow to improve the water quality also for the disease prevention. Results confirmed the curative effect of a 1.0% salt water bath treatment on the early stage of an EJJC outbreak, and the preventive effect on the dietary supplement of ascorbic acid with increasing water quantity before an outbreak.

Our previous suggestion that the gill was a key organ for the development of pseudotuberculosis at the early phase of infection was evaluated in natural infection. From naturally infected amberjack Seriola dumerili groups at two fish farms, total 15 dead fish and total 18 apparently healthy fish were collected. In the dead fish, bacterial isolation rate from the kidney and the detection rates of the pathogen in the gills, kidney and spleen by fluorescent antibody method were 87, 100, 100 and 100%, respectively. In the apparently healthy fish, those rates were 6, 72, 33 and 33%, respectively. The quite high detection rate of the bacteria at the gills of the apparently healthy fish may confirm the suggestion.

Cultured Ryukyu ayu Plecoglossus altivelis ryukyuensis was found to be infected with a microsporidian parasite on Amami Oshima Island in January 2009. The parasite formed numerous cysts on the visceral organs and skin of the diseased fish. High temperature seemed to suppress the development of the parasite; in 2009 and 2010, the disease occurred in the 0-year fish from April to August, and afterwards the prevalence decreased dramatically in September and October. These characteristics well resembled glugeosis in ayu P. altivelis altivelis in other areas of Japan. This parasite seems to be indigenous to Amami Oshima Island, because it was detected in the museum specimens of wild Ryukyu ayu caught in 1991. Average dimensions of spores from Ryukyu ayu were slightly shorter and wider than those of Glugea plecoglossi, but the ranges of the measurements were overlapped. From the above characteristics and molecular analysis of SSU rRNA, it was concluded that the present microsporidian was included genus Glugea, but the specific identity remained to be clarified.

We designed a PCR primer set for specific detection of Miamiensis avidus causing scuticociliatosis in Japanese flounder Paralichthys olivaceus. In the PCR targeting the small subunit ribosomal RNA gene of M. avidus, the expected PCR product with 1,433 bp was amplified from four isolates of M. avidus including three different serotypes, but not from other scuticociliates including Pseudocohnilembus persalinus, P. hargisi and Uronema marinum. Detection limit of the present PCR was 125 fg of genomic DNA. When a group of Japanese flounder suffering the disease was examined by the PCR, 90% of symptomatic fish and 50% of asymptomatic fish were found positive. Thus it is considered that the PCR is useful for detection and identification of M. avidus and consequently for diagnosis of scuticociliatosis in Japanese flounder.

Aquatic animals and their products are among the most widely traded commodities where some 40 percent of global production enters the international market. The international trade in aquatic animals and their products are carried out for various reasons. A number of aquatic animal health threats and risks in the international movement of live aquatic animals include the emergence of new pathogens due to the rapid development of aquaculture, limitations in control options for aquatic animal diseases, occurrence of multi-factorial disease syndromes, frequent sub-clinical infections in aquatic animals, undomesticated status of aquatic animals and little information available on biological requirements and health status, etc. In addition to these, because of the volume of live aquatic animals traded internationally, the diversity of species being moved, the many known and potential pathogens that infect aquatic species, the lack and/or weak enforcement of regulations and in other cases, lack of sector regulations itself– it has been a difficult task to find ways that will reduce the risks of spreading transboundary pathogens. This paper looks at the lessons learned and future challenges in managing the risks of disease incursion associated with the international trade of live aquatic animals.

In December 2006, a Halioticida infection was found in wild mantis shrimp Oratosquilla oratoria in Tokyo Bay, Japan. Fungi were found in the gills of mantis shrimp, isolated from lesions using PYGS agar, and identified by morphological observation and molecular analysis. The fungi formed fragments in the hyphae and several discharge tubes developed from each fragment. Zoospores were formed within the fragments and released into the seawater through the tops of discharge tubes. Based on the characteristics of zoospore production mode, the fungi were classified into the genus Halioticida. Fungal isolates NJM 0642 and NJM 0643, isolated from mantis shrimp, were compared by molecular analysis of the D1/D2 region of the large subunit ribosomal RNA gene (LSU rDNA) with other fungi belonging to Peronosporomycetes, isolated from various marine crustaceans and abalones Haliotis spp. As a result, both isolates were identified as Halioticida noduliformans, which has been isolated from abalone. Moreover, experimental infection demonstrated that the fungus was pathogenic to mantis shrimp. This is the first report of fungal disease caused by Peronosporomycetes in mantis shrimp.

Japanese eel Anguilla japonica and European eel A. anguilla, 65 individuals each, were exposed in a tank to 8,600 oncomiracidia of Pseudodactylogyrus bini and P. anguillae, monogeneans originally recorded on Japanese eel from Asia. Infection was monitored weekly for 6 weeks to compare susceptibility to these monogenean infections between the two eel species. Approximately 40% of the oncomiracidia infected the eels. In the six samplings, both P. bini and P. anguillae were always found in greater numbers on the gills of European eel than on Japanese eel. The first generation of parasites matured within 2 weeks, laying eggs in the tank, and the second generation appeared on the gills of the eels on the third week. European eel was more susceptible not only to the first but also to the second and later generations of parasites than Japanese eel. Besides, both parasites grew faster on European eel than on Japanese eel. This is the first experimental evidence that there are substantial differences in the susceptibility to P. spp. infection between European eel, an unnatural host in Japan, and Japanese eel, the natural host in this country.

Detection limit of PCR was investigated for Renibacterium salmoninarum, the causative agent of bacterial kidney disease, with a logarithmic growth phase. When genomic DNAs from serially diluted bacterial cells were subjected to PCR, the minimum concentration by PCR-detection with 30, 35 and 40 cycles of amplification were all 105 cells/mL, and the sensitivity was not improved by treatments of the bacteria with lysozyme, achromopeptidase and/or SDS. The extraction rate of genomic DNAs from the bacterial cells was approximately 3%. It was confirmed that PCR-detection limit for R. salmoninarum cells mixed with fish kidney tissues was significantly lower than that for the bacteria suspended in the medium. Moreover, there was no significant difference in the detection limit between immunofluorescence antibody technique (IFAT) and PCR. These results suggest that PCR detection should be followed by other methods such as IFAT.

A hitherto unknown leech has been found infected on crucian carps Carassius auratus langsdorfii and C. cuvieri in the Yodo River system since 2000. From the morphological characteristics, the parasite was identified as Limnotrachelobdella sinensis (Piscicolidae). Parasitological surveys on 16 species of wild fish (n = 1,661) caught from October 2000 until March 2005 revealed that the leech was found only from moribund crucian carps. It has a one-year life cycle, in which the leeches were found from December until April next year. Because of its recovery only from moribund fish, large size (up to 4.9 cm in body length) and frequent heavy infection (highest number of parasites/fish: 62), its pathological effects on the hosts were suspected. However, such effects were not made clear except for the hemorrhages and erosion on and near the inner surface of operculum, the attachment site. This is the first record of this parasite from Japanese waters. Since the geographical distribution of the leech in Japan is still restricted to the Yodo River system, the potential risk of spread of the parasite to other water bodies is discussed.