碩士 / 國立臺灣海洋大學 / 水產養殖學系 / 107 / The purpose of this thesis was to study the technologies of management for hard clam farming environment and focused on the effects of adding commercially available photosynthetic bacteria and probiotics to improve the bottom of farming ponds during the whole process. Relevant bacterial species were isolated to clarify the factors of stress that occurred during the farming process. Preliminary investigation might lead to the understanding of the cause of bacterial diseases, the risks of hard clam farming, and the adopting of prevention strategies for disease control to reduce hazards in advance.
In this study, various environmental parameters of water quality and sediment quality were collected during the site visits, and the suspected diseased samples were collected from the ponds where mass mortality occurred for further bacterial isolation. A total of 41 suspected pathogenic strains were obtained. In the pre-challenge test, 15 pathogenic strains were screened out, of these 3 strains could be reisolated basing upon their dominant growth colonies, and the strains were confirmed by biochemical identification and 16S rRNA sequencing. Vibrio spp. were subsequently confirmed as pathogenic strains by a formal challenge test.
Adding photosynthetic bacteria and probiotics after cleaning up the pond bottom could indeed reduce the accumulation of sulfides and the release of hydrogen sulfide, but it could not avoid mass mortality. During the farming process, the drastic changes in temperature and salinity might lead to the weakening of hard clam. The total plate counts and vibrio-like counts could be up to 1000 times between the two different samples. The use of 1 ppm chlorine dioxide could control the spreading of the epidemic. The results showed that the survival rates during harvest in Tainan tended to be higher than that of Changhua, and this may be due to aged ponds and overcrowding, etc. Through the results of the injection challenge test, it could only be judged that multiple bacterial infections might be the cause of death, and the major pathogen(s) still could not be confirmed.
According to present results, the strategy of disease control was to prevent the presence of Vibrio species in the farming environment. It is suggested that the monitoring of vibrio-like counts in the pond should be strengthened during the seasonal conversion, the rainy season and the period of high water temperature in summer. For years, the sediment of pond would gradually become aged. The frequency of flipping the sediment and the time for drying pond should be increased. Before farming, it is necessary to carry out the cleaning up of the pond, and supplementing with the photosynthetic bacteria and probiotics, in order to recover the health of pond bottom. In addition, the improvement of mode of daily management as suggested may reduce the risk of the occurrence of bacterial diseases especially vibriosis.
Keywords: hard clam, mass mortality, vibrio, daily management
| Identifer | oai:union.ndltd.org:TW/107NTOU5086022 |
| Date | January 2019 |
| Creators | Lin, Chia-Hsun, 林佳勳 |
| Contributors | Liu, Ping-Chung, Lee, Kuo-Kau, 劉秉忠, 李國誥 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 103 |
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