DNA barcoding based on a fragment of the cytochrome c oxidase subunit I (COI) gene is widely applied in species identification and biodiversity studies. The aim of this study was to establish a comprehensive barcoding database of coastal ray-finned fishes in Vietnam. A total of 3,638 specimens were collected from fish landing sites in northern, central and southern Vietnam. Seven hundred and sixty-five COI sequences of ray-finned fishes were generated, belonging to 458 species, 273 genera, 113 families and 43 orders. A total of 59 species were newly recorded in Vietnam and sequences of six species were new to the Genbank and BOLD online databases. Only 32 species cannot be annotated to species level because difficulty in morphological identifications and their Kimura-2-Parameter (K2P) genetic distances to most similar sequences were more than 2%. Moreover, intra-specific genetic distances in some species are also higher than 2%, implying the existence of putative cryptic species. The mean K2P genetic distances within species, genera, families, orders and classes were 0.34%, 12.14%, 17.39%, 21.42%, and 24.80, respectively. Species compositions are quite different with only 16 common species among northern, central and southern Vietnam. This may attribute to multiple habitats and environmental factors across the 3,260 km Vietnamese coastline. Our results confirmed that DNA barcoding is an efficient and reliable tool for coastal fish identification in Vietnam, and also established a reliable DNA barcode reference library for these fishes. DNA barcodes will contribute to future efforts to achieve better monitoring, conservation, and management of fisheries in Vietnam.

The cyprinid subfamily Danioninae is one of the most important fish groups due to its inclusion of the model fish, Danio rerio. Molecular investigations have shown that species traditionally placed in the Danioninae are non-monophyletic, divided into two groups corresponding to the Danioninae and Opsariichthyinae. The Danioninae are further divided into three lineages, i.e. chedrins, danionins and rasborins. However, morphological characters determining the foregoing groups are unknown. To investigate the interrelationships among major lineages within the Danioninae, a phylogenetic analysis based on 43 morphological characters from 34 taxa was conducted. Parsimony analysis recovers the Danioninae and Opsariichthyinae to be distinguished by the Y-shaped ligament, absent in the Danioninae while present in the Opsariichthyinae. The Danioninae are divided into two tribes, Danionini and Rasborini. The Rasborini, including Boraras, Brevibora, Horadandia, Kottelatia, Rasbora, Rasboroides, Rasbosoma, Trigonopoma and Trigonostigma, are diagnosed by presence of dark supra-anal pigment and subpeduncular streak as well as presence of the rasborin process on epibranchial 4. The Danionini are composed of two subtribes, Danionina and Chedrina, the Danionina including Chela, Danio, Devario, Microdevario and Microrasbora, and the Chedrina comprising Chelaethiops, Esomus, Luciosoma, Megarasbora, Mesobola, Nematabramis, Opsarius, Raiamas and Salmophasia. The Danionina are diagnosed by the unossified interhyal and presence of the danionin foramen in the horizontal limb of the cleithrum while the Chedrina are characterized by the postcleithrum absent or greatly reduced and approximately normal to abdominal ribs when present.

Phylogeographical analyses on Squalidus argentatus samples from thirteen localities within mainland China and Taiwan were conducted for biogeographic studies, as their dispersal strictly depends on geological evolution of the landmasses. A total of 95 haplotypes were genotyped for mtDNA cyt b gene in 160 specimens from nine river systems. Relatively high levels of haplotype diversity (h = 0.984) and low levels of nucleotide diversity (π = 0.020) were detected in S. argentatus. Two major phylogenetic haplotype groups, A and B, were revealed via phylogenetic analysis. The degree of intergroup divergence (3.96%) indicates that these groups diverged about 4.55 myr (million years) ago. Haplotype network and population analyses indicated significant genetic structure (FST = 0.775), largely concordant with the geographical location of the populations. According to SAMOVA analysis, we divided these populations into four units: Yangtze-Pearl, Qiantang-Minjiang, Jiulong-Beijiang and Taiwan groups. Mismatch distribution analysis, neutrality tests and Bayesian skyline plots indicated a significant population expansion for lineage A and B, approximately dated 0.35 and 0.04 myr ago, respectively. We found strong geographical organization of the haplotype clades across different geographic scales that can be explained by episodes of dispersal and population expansion followed by population fragmentation and restricted gene flow.

A new genus and species, Sinorhodeus microlepis gen. et sp. nov., is described from a tributary of the Yangtze River, in Chongqing City, China. Sinorhodeus gen. nov. can be distinguished from four closely related genera, Paratanakia, Pseudorhodeus, Rhodeus, and Tanakia, by the following combination of characters: pharyngeal teeth 0,0,4-4,0,0, longitudinal scales 41-46, white spots on dorsal-fin rays absent, a black blotch on dorsal fin in juvenile absent, and less developed wing-like yolk sac projections in larvae. Phylogenetic analysis of one mitochondrial gene and six nuclear genes supports the establishment of the new genus.