| 英文摘要 |
The flathead mullet, Mugil cephalus, is a commercially important fish for both fisheries and aquaculture in Taiwan. Based on genetic analysis, three cryptic species of M. cephalus were identified inhabiting the Northwest Pacific (namely NWP1-3). These species present a sympatric distribution in Taiwanese waters and studies showed that each cryptic species has its own unique reproductive characteristics. The roe development potential of the species, therefore, has become a critical selection criterion for local aquaculture. In this study, the roe development and somatic growth of different M. cephalus cryptic species were investigated from a local aquaculture pond in tropical Southern Taiwan with fingerlings from nearby estuarine waters. All the sampled fish were identified as NWP2 or NWP3 with the use of mitochondrial haplotype specific PCR (MHS-PCR) screening. NWP2 was the main species cultured from our study pond, which had a high gonadosomatic index (GSI 10-20˜, n=15) after culturing for two years and harvesting in November. Most NWP3 sampled from the same aquaculture pond had the same age as NWP2 but with limited roe development (GSI <0.1-3˜, n=11), except for the biggest NWP3, which had a similar GSI value as NWP2 and an otolith ageing of 3+ years. Both species can grow to around 408.5-483.9 mm in fork length with 930-1,630 g in weight after being cultured for two years. In order to offer a comprehensive understanding of how cryptic species differ in their reproductive biology and growth, these parameters were compared among cultured fish by other studies as well as collected data from the fields during 2005-2015. We concluded that even after 10 years, the spatial genetic structures haven't changed for M. cephalus cryptic species. The varied gonadal development levels of the same M. cephalus cryptic species cultured in different climate zones suggested their gene expression plasticity for adaptation. |
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