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.
We evaluated the effect of rearing temperature (13 and 17°C) on the toxicity of Poly(I:C) against Japanese flounder Paralichthys olivaceus (mean BW 8.2 g). In the fish reared at 17°C, we observed signs of toxicity such as redness or ulceration of the skin around the inoculation site or death in 41.7%, 16.7%, 16.7% and 0% of the fish injected with 800, 400, 200 and 100 μg Poly(I:C)/fish, respectively. In the fish reared at 13°C, we observed signs of toxicity in 83.3%, 75.0%, 25.0% and 33.3% of the fish that were injected with 800, 400, 200 and 100 μg Poly(I:C)/fish, respectively. Our results suggest that the toxicity of Poly(I:C) is higher in Japanese flounder reared at 13°C than in those reared at 17°C.
Japanese flounder Paralichthys olivaceus were immunized intraperitoneally with formalin-killed cells (FKC) prepared from serotype I or II of Streptococcus parauberis. Three weeks after immunization, the fish were challenged with the homologous or heterologous serotype by subcutaneous or intravascular injection. Both serotype FKCs proved to be effective against the challenges with the homologous isolate [relative percent survival (RPS) values: 100%], whereas RPS values in the fish challenged with the heterologous serotype isolates varied from 0% to 100%. These results suggested that each serotype FKC has insufficient cross-protective efficacy against the other serotype.