基于COI基因的福建近海部分仔稚鱼DNA条形码分析

摘要

Fish eggs, larvae, and juveniles are important food sources for fish populations. Correct identification of fish eggs, larvae, and juveniles can let us understand which species are spawning where and when, their hatch-ing and nursery grounds, and their possible migration routes during their early life history. At present, fish larval and juvenile identification mostly relies on morphological characters. But since different species often share simi-lar characters and species change greatly during their early development stages, identification of fish larvae and juveniles is very hard, most of which can only be identified to the family or genus level, except for a few fish ju-veniles that can be identified to species. Moreover, because traditional morphological methods rely too much on personal experience and observation methods, it is easy to misidentify fish larvae and juveniles and difficult to identify to the genus or species level. In view of the limitations of traditional morphological methods, DNA bar-code techniques could be a rapid tool to survey many uncertain species, species composition, and cryptic species and to distinguish morphologically similar species. To study the applicability of this technique to identify fish larvae and juveniles, samples were collected in Fujian coastal areas from July 17 to 20, 2015, and 80 samples were selected for DNA barcoding analysis. A total of 73 valid cytochrome C oxidase subunit I (CO I) gene sequences of fish larvae and juveniles in Fujian coastal areas were obtained. Five species were identified to the level of genus, two were identified to the level of family, and another 26 species were identified to the level of species. The re-sults showed that the average Kimura-2-parameter (K2P) distances within species, genus, family, and order were 0.0023, 0.1797, 0.1937, and 0.2420, respectively. The interspecific genetic distance was much larger than the in-traspecific distance, and K2P genetic distance values increased with taxonomic level. All sequences formed spe-cies units in a neighbor-joining phylogenetic tree, indicating that the DNA barcode can be used to identify these 33 species. Consequently, CO I barcoding is one of the useful tools to identify fish larvae and juveniles. However, this test highlights the limitations of DNA barcoding. The neighbor-joining tree cannot analyze cluster relations clearly above the taxonomic level of family, which corresponds to the slower-increasing trend of genetic distance values with the higher taxa. This means that CO I barcoding is only suitable for phylogenetic analysis of lower taxa, and is not applicable for species identification of higher taxa. Four sequences having high similarity (greater than 98%) with many species in the database were identified only to genus (Gerres sp., Epinephelus sp., Auxis sp., and Saurida sp.). That indicates that some fish species are similar not only in shape but also in CO I sequences, and sequence identification cannot be done using only CO I barcoding. We should strengthen the research of multi-gene barcode technology in order to overcome the deficiency of the single CO I gene sequence. Another sequence, limited by the number of sequences that can be used in the DNA database, with a maximum similarity between 85%-86%, was identified to the level of family. It is suggested to further improve the sequence quantity and quality of the DNA barcode database, so as to let it be more useful for species identification.%为研究DNA条形码技术在遭遇瓶颈的仔稚鱼种类鉴定中的适用性,2015年7月17-20日采集福建近海仔稚鱼样品,并挑选80尾进行DNA条形码分析.获得仔稚鱼的CO I基因序列73条,鉴定仔稚鱼26种,隶属于7目22科25属,另有5个物种仅鉴定到属,2个物种仅鉴定到科.种内平均遗传距离为0.0023,属内种间遗传距离为0.1797,约为种内遗传距离的78倍,说明利用CO I基因可以进行有效的仔稚鱼物种鉴定.科内属间、目内科间的遗传距离分别为0.1937、0.2420,遗传距离随着分类阶元的提高而增大.在系统进化树的分析中,同一种类的不同个体都聚在一支,所有物种都分别聚为独立的一支,这些物种都能有效区分开来.以上结果表明,线粒体CO I基因作为DNA条形码可以实现仔稚鱼的物种鉴定,且较多能鉴定到种的水平.