博士 / 國立臺灣海洋大學 / 水產養殖學系 / 106 / Mugil cephalus is an important aquaculture species in Taiwan because of its highly valuable roe. In order to produce large numbers of ovaries of an adequate size, the mullet fry are captured from the wild and then raised in aquaculture ponds until maturity. However, not all females develop ovaries and some only develop small ovaries. Thus, it seems likely that genetics plays an important role in how the various mullet populations found in Taiwan waters mature and produce such a wide variety of roe sizes under identical aquaculture conditions. The aim of the study is the identification of useful genetic markers for selecting mullet that produce large roe under aquaculture conditions. The correlation of ovary size, body size and gonadosomatic index (GSI) with each mtDNA profile of the cultured mullet has been investigated in detail. The presence of further hidden genetic structure that could help to explain the differences of roe size across mullet populations around Taiwan is also explored by using microsatellites.
Three cryptic species of Mugil cephalus (NWP1, NWP2 and NWP3), identified using the multiplex cytochrome oxidase subunit Ⅰ (COⅠ) haplotype-specific PCR, were cultured in aquaculture ponds. The NWP1 females generally have the largest body size, but fail to have developed ovaries by 3 years of age. After an additional year of culture, the NWP1 females were found to yield only small ovaries. By way of contrast, the NWP2 females, which have the smallest body size, generally yield larger ovaries with the size of the roe depending on the age of the fish, 2, 3 or 4 years old. The rarest mitotype, NWP3, produce significantly larger ovaries, as well as a bigger body size, at 3-years old than 3-year-old NWP2 females. Thus, both NWP2 and NWP3 fry can be considered to be suitable subjects for mullet aquaculture. On the other hand, NWP1 fry are not suitable for aquaculture over 3 years or 4 years on economic reasons and should be left as a fishery resource in the sea if possible.
The nuclear population genetic structure has also been analyzed using ten microsatellite loci. The sampled Taiwanese populations, whether classified temporally or geographically, was found to be highly dynamic and genetic differentiation into sub-populations at a nuclear DNA levels was found, in addition to the above differentiation on mitotype. However, the level of genetic differentiation on average was weak, FST=0.029. Either the lack of allele fixation or the genetic admixture might occur between the NWP1 and NWP2 mullet, while the NWP3 mullet is the most genetically differentiated. Although the genetic diversity of the NWP1, NWP2 and NWP3 populations showed no recent bottleneck under the strict model used, each mitotypic population may be vulnerable to the increasing fishing pressure, as well as the climate change, in a long term. Thus, the practice of conservation management for the mullet fishery resource is required since M. cephalus are exploited both by capture fisheries and aquaculture in Taiwan.
| Identifer | oai:union.ndltd.org:TW/106NTOU5086001 |
| Date | January 2018 |
| Creators | Angela Chien, 簡名瑀 |
| Contributors | Sheen, Shyn-Shin, Ralph Kirby, 沈士新, 柯比 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 122 |
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