| Summary: | 碩士 === 國立臺灣大學 === 動物學研究研究所 === 93 === The cutlassfish (Trichiurus spp.) is a group of ribbon-like demersal fishes inhabited in continental shelf with high commercial value in the world. The most important species is the cosmopolitan one, Trichiurus lepturus, which distribute across tropical and subtropical waters worldwide. Most of the commercial catches of cutlassfish come from the shelf regions of northwest Pacific, in which area the landings accounted to 80% of the world catches.
Previous studies indicate that, one species of the Trichiurus occurred in the regions of northwest Pacific. In recent studies, three species have been added to taxonomic and faunal lists in the region. In the waters around Taiwan, there were 2 phenotypes can be identified similar to T. lepturus, however it is contentious that 2 phena or 2 species should be estimated from morphological and biogeographic analysis. In this study, I apply quantitative methods to analyze morphological characters and molecular markers dually, and expect to solve those taxonomic problems and to clarify the nomenclature status of Trichiurus. The results showed that there are three valid species identified in our samples collected from the vicinity waters around Taiwan; T. lepturus, T. nanhaiensis and T. brevis. Trichiurus brevis is the most distinctive among the three species by having less than 35 dorsal fin elements, and the separation of T. nanhaiensis from T. lepturus is based on fusion or not of forntal bone. Principal component and discrimination function analysis confirmed previous finding with statistical significance (<0.3% mis-identification). Partitioning of molecular variance indicated that more than 10% of variations were ascribed to inter-specific, and the specific taxonomic status is firmly supported.
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