The genus of Upeneus (Perciformes: Mullidae) up to 46 goatfish species worldwide and widely distributed in tropical and subtropical ocean area (Uiblein and Gouws 2014; Nelson and Mark 2016; Uiblein and Motomura 2021). In China, the goatfishes species diversity were decreased with latitude, such as only one species U. japonicus was recorded in the Bohai Sea and the Huanghai Sea (Jiao and Chen 2000), including U. tragula, U. vittatus, U. subvittatus, U. sulphureus, U. quadrilineatus, U. moluccensis, U. japonicus, U. luzonius and U. heterospinus (Cheng et al. 1962; Shen 1993; Chen and Zhang 2015; Uiblein et al. 2019). Goatfishes sometimes are difficult to accurately identify based on the morphology method because the color patterns of different stages of development was unclear, and fading and discoloring of body color after death (Pavlov and Emel Yanova 2018). Using DNA barcoding technology can provide some level to reduce the difficulty of identification and enhance the accuracy of identification (Yi et al. 2018; Sharifuzzaman et al. 2021).
The South China Sea, as the most significant water area in China, possesses complex habitats to provide various marine organisms with a well living environment, leading to abundant biological resources in the South China Sea (Shan et al. 2021). However, an underestimated species diversity is not conducive to the protection of biodiversity and biological resources. Therefore, our study intends to close the knowledge gap by contributing to the taxonomy of the genus Upeneus in the South China Sea.
Specimens were collected from local fish markets near the northwestern South China Sea. Specimens and tissue samples were deposited at the College of Fisheries, Guangdong Ocean University (sampling sites see table S1). The counts and measurements were based on Uiblein and Heemastra (Uiblein and Heemstra 2010). COI gene was amplified by PCR using the two pairs universal primers from Ward et al. (Ward et al. 2005), and the PCR products were sequenced by Sangon Biotech (Shanghai). Thirty-three sequences were aligned and manually edited using Sequencher 5.4.5 (Gene Codes Corp., America). These sequences were deposited in GenBank (MZ513942-MZ513973 and MZ514010). Kimura 2-parameter (K2P) model was employed to construct the neighbour-joining (NJ) tree and calculated the genetic distances by MEGA 6.0. The maximum likelihood (ML) tree was constructed using IQ-TREE (Nguyen et al. 2015) under the best-fit model, HKY+G4+F selecting BIC criterion by ModelFinder (Kalyaanamoorthy et al. 2017) for 5000 ultrafast bootstraps (Minh et al. 2013) and 1000 replicates of Shimodaira-Hasegawa test (SH-aLRT) (Guindon et al. 2010). The IQ-TREE and ModelFinder were plugins in PhyloSuite v1.2.2 (Zhang et al. 2020). All homologous sequences of Upeneus were from GenBank. Automatic Barcode Gap Discovery (ABGD) was carried out on the website with default parameter (https://bioinfo.mnhn.fr/abi/public/abgd/). Information of specimens and COI sequences are provided in Table S1.
Morphometric measurements of U. spottocaudalis and U. sundaicus was shown in Table 1. Upeneus spottocaudalis was firstly recorded in the southern Indonesia and the northeastern Australia (Uiblein et al. 2017), and Fricke (Fricke et al. 2019) found the distribution extended to the New Ireland. This species with VII spines in the first dorsal-fin are divided into japonicus-group; head and body dorsally reddish; mid-lateral body with a faint reddish band extending the upper base of caudal-fin; series red blotches on the body; barbels yellow; lower caudal-fin with rounded or triangular dark spots or blotches is the key taxonomic features to distinguish with other species of japonicus-group, which only are with oblique stripes in lower caudal-fin (Fig. 1a). Upeneus sundaicus with VIII spines in the first dorsal-fin belongs to tragula-group; head and body dorsally pale brown; a blonder brown stripe on the mid-lateral body from behind the upper operculum to the base of the caudal-fin; barbels yellow; lower caudal-fin without any spot or stripe; upper caudal-fin with series weak stripes (Fig. 1c).
The phylogenetic tree (Fig. 2) shows that our sequences of U. spottocaudalis were clustered with the sequence (GU673189) of paratype of U. spottocaudalis. Furthermore, the U. sundaicus sequences in this study of were clustered with the sequences identified as U. sundaicus from GenBank. These two results were also presented in the NJ tree. All of these clades were supported with high value of SH-aLRT, and ultrafast bootstrap. The intraspecific genetic distances of U. spottocaudalis (0.2%) and U. sundaicus (0.3%) were much less than 2% (Table S1). Result of classification based on ABGD was concordant with the ML tree and the NJ tree (Fig. 2).
Taxonomy is the most basic subject in biological studies, and accurate species identification determines the feasibility of subsequent studies. Two new records species of U. spottocaudalis and U. sundaicus were identified integrating morphology and DNA barcodes, which enrich the diversity of ichthyofauna of the South China Sea. It is of certain reference value to the taxonomy of the genus Upeneus in the South China Sea.