Abstract:

Six Thryssa species were collected from Chinese coastal waters for morphological description and phylogenetic relationships analysis. Results indicated that the position of maxillary extend and number of lower gill rake in the first gill rake were the main morphological characteristics for the identification of six Thryssa species. Mitochondrial COI gene fragments were amplified and sequenced for thirty individuals of Thryssa species. A 525 bp sequence was obtained, containing 175 variable sites, which determines 172 parsimony informative sites, 3 singleton sites, no indels/deletions, 182 transitions, and 57 transversions. An obvious anti-G biasness was noted from the base composition of A and T higher than that of G and C. Comparing homologous sequences from GenBank with our study validates that there are variations among Thryssa species based on the COI sequence. Moreover ten absolute groups were also identified in all sequences based on genetic differences in amino acids and genetic distances between groups. However, this requires further investigation to determine whether there are uncovered cryptic species. The NJ tree indicated that T. setirostris was the first species derived from the genus, and sequences of T. mystax were disorderly clustered with that of T. vitrirostris. The divergence date of Thryssa species presented here is early Miocene. It is suggested that more molecular markers be needed to clarify variations in T. mystax and T. vitrirostris in the future.

Key words: Thryssa, phylogenetic relationship, DNA barcoding, genetic distance, morphology