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.
Isolation of pathogens is essential for studies on infectious diseases. Present study aimed to develop an effective method for culture isolation of koi herpesvirus (KHV). KHV was effectively isolated using CCB cells only from fish with clinical signs. KHV survived longer at 4°C or -30°C than at 23°C in fish tissues. These results suggest that KHV can be isolated from symptomatic fish kept at the low temperature. To increase isolation efficiencies, the brain as well as the gills and kidney should be included in target organs for examination. In addition, freezing of the organs at -30°C or -85°C is recommended when samples are preserved for a long period before isolation.
In Korea, mass mortalities occurred among cultured common carp Cyprinus carpio in 1998. Moribund fish showed clinical signs like those of koi herpesvirus (KHV) disease. In this study, we applied in situ hybridization (ISH) method to detect KHV DNA in paraffin-embedded tissue specimens that had been prepared from the moribund carp of nine fish farms at four different regions in 1998. ISH-positive cells were found in various tissues including kidney, spleen, heart, liver, gills and intestine from eight fish farms. Our results suggest that the mass mortality of carp in 1998 was associated with KHV infection and thus KHV was introduced into fish culture farms in South Korea in 1998 or earlier.