DNA barcoding reflects the diversity and variety of brooding traits of fish species in the family Syngnathidae along China’s coast

• This study provided a systematic diversity of syngnathid fishes along China’s coast.
• There was a variety of brooding traits among the Syngnathidae fishes.
• Seahorse and pipefish sequences showed high frequencies of nucleotide substitutions.

DNA barcoding offers a rapid and accurate assessment for species labelling and identification. Here, we investigated the performance of DNA barcodes in a sample of Syngnathidae, a unique group of fish with male pregnancy. A total of 1002 DNA barcodes using 649 base-pair fragments of the cytochrome c oxidase subunit I (COI) gene were generated. All species were associated with distinct DNA barcode and could be readily distinguished; seven of the COI barcode clusters represented the first species records submitted to the Barcode of Life Data Systems (BOLD) and GenBank databases. In the Neighbor-joining tree of COI sequences, two major clusters (Gastrophori and Urophori) were displayed, which could also be classified by their brood pouches. However, the tail-brooding Hippichthys cyanospilus and trunk-brooding Syngnathoides biaculeatus were reverse-clustered together with the Gastrophori and the Urophori, respectively. Both seahorse and pipefish sequences showed high frequencies of nucleotide substitutions. The probability of nucleotide substitutions, those in pipefish were higher than that of all seahorses. However, we identified no signal for positive selection based on the COI gene in any of the data sets. Our results supported DNA barcoding as an efficient molecular tool for achieving better monitoring, conservation, and management of fisheries.