The anti-bacterial substance, AVS-03d, isolated from the culture of marine Pseudoalteromonas sp. A1-J11 was separated by HPLC with a C18 column. The chemical structure of AVS-03d was identified as 2-n-pentyl-4-quinolinol (C14H17NO = 215.13) on the basis of mass spectrometry and NMR spectroscopy. AVS-03d showed strong inhibitory activity against Vibrio harveyi strains as compared with other quinolinol compounds, suggesting that the length of the alkyl side chain of the compound is important for anti-bacterial activity.
Flounder herpesvirus (FHV) induces epidermal hyperplasia in larval Japanese flounder Paralichthys olivaceus. We examined the influence of ambient oxygen and salinity concentrations on mortality of flounder larvae by FHV infection. FHV-infected fish showed markedly higher mortality than uninfected fish under normoxia (partial oxygen pressure; PO2 = ca. 160 Torr), but survived at high rates under hyperoxia (PO2 = ca. 280 Torr or higher) as in uninfected fish. In the PO2 range from 100 to 400 Torr, infected fish always displayed lower levels of oxygen consumption (MO2) compared to the uninfected fish. Under PO2 of 260 Torr, the 48 h-survival rate of infected fish in diluted seawater (salinity 8 or 16 ppt) was much higher than that in full-strength seawater (salinity 32 ppt). Whole-mount immunocytochemistry to detect Na+/K+-ATPase and Na+/K+/2Cl- cotransporter of the skin of both infected and uninfected larvae revealed that the infected larvae had a significantly lower number of chloride cells. These results suggest that flounder larvae infected with FHV die of dysfunction in respiration and osmotic regulation.
Viral endothelial cell necrosis of eel (VECNE) of Japanese eel Anguilla japonica, caused by an adenovirus (JEAdV), has been a serious problem of aquaculture industry in Japan. In the present study, effectiveness of increasing water temperature and non-feeding against VECNE was evaluated. Cumulative mortalities of fish intraperitoneally injected with 105.05 TCID50/fish of JEAdV increased with elevating water temperature in the range between 20°C and 31°C, but mortality at 35°C was as low as that at 20°C. Rearing infected fish under the non-feeding condition further enhanced the effect of treatment at 35°C. The effectiveness was dependent on rearing periods at the high temperature; more than 3 days at 35°C were needed to reduce mortality. Fish, which survived the primary challenge with JEAdV at 35°C, showed high resistance to re-challenge with JEAdV. From these results, the treatment of fish under the non-feeding condition at 35°C is useful to control VECNE.
Common carp Cyprinus carpio were experimentally exposed to koi herpesvirus (KHV) under water temperature regimes ranging from 16°C to 28°C. Fish maintained at 16°C, 23°C and 28°C died due to infection at 21-52, 5-20 and 7-14 days post-virus exposure (dpe), respectively. Cohabitation experiments in which KHV-infected common carp were kept with naive koi carp revealed that infectious virus was continuously shed from the infected common carp for 34 days (7-40 dpe) at 16°C, for 14 days (1-14 dpe) at 23°C and for 12 days (3-14 dpe) at 28°C. The relatively extended duration of virus shedding observed at 16°C suggests the potential risk of infection from fish maintained under low-temperature conditions as a source of viral inocula.
A study was carried out to estimate the time for Nocardia seriolae infection of cultured yellowtail Seriola quinqueradiata. Yellowtail (58-1600 g in body weight) were collected at two fish farms in Ehime Prefecture from July 2001 to May 2002. Serum antibodies against N. seriolae antigens were detected by indirect enzyme-linked immunosorbent assay (ELISA). A significant increase in the serum antibody level was first recognized in August 2001, and high antibody levels were maintained in fish of both farms. Outbreaks of nocardiosis in the farms initiated in September or October and terminated in November. These results suggest that infection of N. seriolae in yellowtail began between July and August.
In 1998 and 1999, severe episodes of mortality, often reaching 90%, were recorded among cultured populations of ayu Plecoglossus altivelis reared in Japan. The diseased fish showed appetite reduction and abnormal swimming behavior. Histopathological examination revealed proliferative branchitis with enlarged and atypical epithelial cells. Abundant electron-dense, virus-like particles were observed within the cells under transmission electron microscopy. The particles had a cocoon-like shape and ranged in length from 200 to 300 nm, indicating a member of the poxvirus group. These findings suggest the possibility that the mortality events are related to infection of a poxvirus-like virus.