博士 / 國立臺灣大學 / 動物學研究所 / 89 / White spot syndrome virus (WSSV) has been detected in cultured and captured shrimps, crabs, pest crabs and other arthopods. In this study, healthy Marsupenaeus japonicus and Penaeus monodon juveniles were immersed in a sub-lethal dose of filtrate prepared from diseased or healthy shrimp. After 10 days, the sub-lethally infected and the healthy control shrimp were both subjected to different temperature conditions. The experimental groups of both shrimp species began to die of high temperature (29 oC) treatment, while at low temperatures (15 oC) the mortalities were lower. With an initial exposure to low temperatures for 24 h, after which the water temperature was increased to 24 or 29 oC, P. monodon mortality reached 90%-100% at either temperature, while at 29 oC, M. japonicus mortality reached 100% within a further 48 h, but only reached 40% at 24 oC. The moribund experimentally infected shrimp under temperature shifts were all one-step WSSV PCR positive. These results demonstrate that temperature shifts alone can induce an outbreak of WSS disease in populations in which viral infection is only two-step WSSV positive.
In order to discover the pattern of growth and survival of WSSV-infected shrimp on typical shrimp farms, as well as the interaction between the cultured shrimp and endemic WSSV carrier, a field survey of WSSV infection in cultured shrimp in 25 ponds in southern Taiwan at two-week intervals was carried out. Out of 25 ponds, 13 were successfully harvested. Only 2 out of 25 ponds were found to be 2-step PCR negative during the growth period. Even though the ponds were harvested in which WSSV-infected poatlarvae during growth period was detected, the survival rate, the yield, and the average body weight were variable. Mass mortality will predictably occur for any pond stocked with WSSV-infected postlarvae. At high density (>50pcs/m2), no ponds were harvest in our survey. Because the host range of WSSV is wide and hard to eliminate completely from the open culture system, it is important to monitor both the post-larve before stocking and larvae carefully during the growth period by WSSV diagnostic PCR.
We re-tested stored (frozen) DNA samples in five independent PCR replicates and confirmed that equivocal tests results from a previous study on WSSV in brooders and their offspring arose because amounts of WSSV DNA in the test samples were near the sensitivity limits of the detection method. The prevalence of WSSV among spawners was 67% before spawning and 80% after. This could demonstrate that spawning stress may trigger WSSV replication. Only 60% of brooders spawned successfully, and those heavily infected when captured mostly died within 1 to 4 days, but only 20% managed to spawn. All their egg batch sub-samples were 1-step PCR positive, and many failed to hatch. The spawning rates for lightly infected spawners and negative spawners were high (81 and 78%, respectively). None of the negative spawners became WSSV positive after spawning, and none gave egg samples positive for WSSV. A full 47% of lightly infected brooders became heavily infected after spawning, and almost all egg sample replicates (89%) tested 2-step PCR positive. They remained lightly infected brooders after spawning, and only 31% of their egg sample replicates were 2-step PCR positive. Based on these results, we recommend that to avoid false negatives in WSSV PCR brooder tests, screening tests should be delayed until after spawning. We also recommend, with our PCR detection system, discarding all egg batches from brooders that are 1-step PCR positive after spawning. On the other hand, it may be possible with appropriate monitoring to use eggs from 2-step PCR positive brooders for production of WSSV free or lightly infected PL. This may be used to stock shrimp ponds under low stress rearing conditions.
| Identifer | oai:union.ndltd.org:TW/089NTU00312033 |
| Date | January 2001 |
| Creators | Hui-Chen Hsu, 許惠貞 |
| Contributors | Guang-Hsiung Kou, Chu-Fang Lo, 郭光雄, 羅竹芳 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 116 |
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