| Summary: | 碩士 === 國立臺灣大學 === 動物學研究所 === 88 === In Taiwan, high mortality of cultured Pacific white shrimp, Litopenaeus vannamei, juveniles occurred within 3 days of disease onset in March, 1999. Moribund juveniles had a soft shell and a pale reddish coloration and survivors were found with multifocal, melanized, cuticle lesions on the cephalothorax. Prominent necrosis in the cuticular epithelium and subcutis had pyknotic nuclei and cytoplasmic spherical inclusion that gave lesions a peppered or buckshot-riddled appearance. In situ hybridization analyses using Taura syndrome virus (TSV)-specific cDNA probes showed that 87% of the juveniles examined were TSV positive. Negative staining of the purified viral preparations revealed the presence of icosahedral particles, 28-31nm in diameter. These results indicate that TSV is responsible for the acute mortality of white shrimp in Taiwan. TSV may have been introduced to Southeast Asia with chronically infected brooders or asymptomatic carriers imported from the Western Hemisphere.
Study was further conducted to examine the changes in hemoplasma of Pacific white shrimp L. vannamei artificially infected with TSV. Hemoplasma obtained from infected and control shrimps were analyzed for bacterial agglutinating titer, antibacterial activity, plasma clottable protein concentration, plasma hemocyanin content, plasma Mg++/Ca++ level. Acute TSV infection caused high mortality in Pacific white shrimp and the survival rate was 0 % on the day sixth post infection. Hematological results showed plasma hemocyanin content, plasma Ca++ level and clottable protein content significantly decreased as disease progressed by TSV infection. A significant increase in plasma Mg++ level was found toward second day of TSV group. There is no antibacterial activity in the plasma of both control group and the day 0 of TSV group. However, on the day second and fourth after TSV-infection, we can detect the antibacterial activity against V. harveyi in the plasma. These results indicate that some hemoplasma parameters changed after TSV infection and they probably could be useful as the indicators of healthy status.
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