Mitogenomes confirm first Chinese records of short-tail stingrays

Two mature short-tail stingrays caught as bycatch in the East China Sea provide the first formal records of Bathytoshia brevicaudata from China, according to a study combining detailed morphology, stomach-content analysis, complete mitochondrial genomes and a broad phylogenetic reconstruction. The male and female were collected during bottom trawling off northern Zhejiang in March 2025 and weighed 42 and 60 kilograms, respectively. Their identification expands the documented Chinese chondrichthyan fauna and reveals new information about sexual differences, feeding, potential movements between marine environments and the evolutionary position of a species whose biology remains poorly understood.

Bathytoshia brevicaudata was originally described from New Zealand and has a geographically disjunct distribution that also includes southern Africa, southern Australia and New Zealand, and temperate northwestern Pacific waters. The northwestern Pacific population was historically treated as a separate species, Dasyatis matsubarai, but subsequent morphological and molecular research synonymized that name with B. brevicaudata. Recent records from South Korea and southern Japan have documented the species beyond its formerly understood range.

A specimen collected near Lanyu Island, Taiwan, in 1987 and initially identified as D. matsubarai was later judged likely to be Pteroplatytrygon violacea after photographic examination, leaving the Zhejiang animals as the first verified Chinese records of B. brevicaudata. The two Zhejiang specimens were deposited as vouchers ZJOUMBM F00035 and ECSFRI 28263. The male measured 1,810 millimeters in total length and had a disc width of 1,060 millimeters, while the female measured 1,955 millimeters and had a disc width of 1,295 millimeters.

Both had broad rhombic discs, short blunt snouts, small pelvic fins, stout rather than whip-like tails, pale gray dorsal surfaces and white ventral surfaces. Diagnostic white pores ran diagonally from the pectoral-fin bases toward the leading edges, and the tail carried rows of thorns and tubercles around a single caudal sting. The relatively short tail and conspicuous pores distinguished the animals from B. lata, a large ray that has historically dominated records from Chinese waters.

Close examination of the preserved material documented sex-associated differences that are relevant to future identification. The mature male had nine large backward-pointing tubercles on the back, compared with three in the female. Its mouth floor carried seven transverse rows of oral papillae, whereas the female had five; the male also had three prominent central papillae and the female four.

The male’s teeth ended in sharp cusps, while the female’s were blunt and rounded. The male’s claspers measured 257 millimeters and were robust, rigid and fully calcified, supporting its classification as an adult. The researchers proposed that sharper male dentition might assist with capturing agile prey, but noted that this functional interpretation requires further evidence.

Stomach analysis of the dissected female contained fragmentary prey, including two horsehead tilefish, Branchiostegus japonicus, one Japanese jack mackerel, Trachurus japonicus, and one specimen of the benthic fish genus Neobythites. One identifiable tilefish exceeded 30 centimeters in total length. This finding extends the documented diet beyond the previously stated emphasis on invertebrates and small fishes and demonstrates that an adult female can consume substantially larger teleosts.

Because the observation came from one animal in one location, however, it cannot establish the species’ complete dietary range; the authors instead suggest that diet may vary with body size and geographic location. The stomach also contained three longline fishing hooks: two J hooks lodged in the lumen and a circle hook that passed through the gastric wall into the liver. The two hook types are associated with different fishing operations, with J hooks linked to coastal fishing and circle hooks to pelagic longlines.

Their co-occurrence provides physical evidence that the female had visited areas used by distinct fisheries, consistent with movement between the continental shelf and oceanic waters. The authors connect this possibility to the East China Sea and the Tsushima Strait, where cold water flowing southward may create a route for dispersal, but the hooks alone do not establish a complete migration route or population-wide movement pattern. Complete mitochondrial sequencing showed that the female and male each had a 17,640-base-pair mitogenome, deposited in GenBank as PV699610 and PV699611, respectively.

Each genome contained 37 genes—13 protein-coding genes, 22 transfer RNAs and two ribosomal RNAs—plus a control region. Most genes occurred on the heavy strand, whereas ND6 and eight transfer RNAs were encoded on the light strand. The assemblies had nearly identical organization, gene lengths, codon usage and nucleotide skews, including an overall adenine-thymine content of 59.2 percent, a pattern consistent with other dasyatid rays.

These mitogenomes were the first complete sequences from the Chinese specimens, although complete mitochondrial genomes from the species had previously been reported from South Korea. The two transfer-RNA and ribosomal-RNA sets also showed structural consistency. All 22 transfer RNAs were predicted to form the usual cloverleaf secondary structures except trnS1, which lacked the dihydrouridine arm.

The 12S and 16S ribosomal RNA genes measured 964 and 1,696 base pairs. Across all 13 protein-coding genes, the ratio of nonsynonymous to synonymous substitutions was far below one, consistent with purifying selection. ATP8 had the highest ratio at 0.1903 and COX2 the lowest at 0.0302.

The Chinese animals also showed no variation at the COI marker relative to the available South Korean B. brevicaudata sequence and only minimal ND2 divergence of 0.001010101, supporting their assignment to the same species and apparently the same northwestern Pacific population. The researchers reconstructed a myliobatiform phylogeny using 15 mitochondrial genes from 52 species, with Narcine timlei and Rhinobatos schlegelii designated as outgroups. Bathytoshia brevicaudata grouped with the Atlantic B. centroura, while B. lata was more divergent.

Mean COI p-distance between B. brevicaudata and B. centroura was 0.0375, compared with 0.0797 between B. brevicaudata and B. lata and 0.0620 between B. centroura and B. lata. In the complete tree, Pteroplatytrygon was nested within Bathytoshia, implying that Bathytoshia is not monophyletic under the mitochondrial dataset. This differed from an earlier phylogeny based only on COI, and the researchers said the relationship remains to be clarified with further sampling.

The wider analysis also detected unexpectedly high variation within B. lata, whose mean COI intraspecific p-distance was 0.0831. The largest value, 0.180579, separated a sample from Sri Lanka from one from Spain, while samples from India and Sri Lanka differed markedly from those in other seas. The authors proposed that some South Asian samples could constitute a distinct evolutionary group, but stressed that local voucher specimens are required to validate that interpretation.

The finding illustrates both the resolution provided by broad mitogenomic sampling and the need to connect genetic records to reliably identified physical specimens before drawing firm conclusions about species boundaries or population structure. The findings therefore establish occurrence and provide a reference for morphology, mitogenomes and feeding observations, but they do not establish abundance, breeding sites, nursery habitat, population structure or the prevalence of the movements suggested by the fishing hooks and prey remains. Broader sampling across the East China Sea and neighboring regions will be needed to determine how widespread the species is and how its populations are connected.

Subject of Research: First verified Chinese records of Bathytoshia brevicaudata based on morphology, stomach contents and mitogenomic analysis

Article Title: First records of Bathytoshia brevicaudata (Hutton, 1875) ( Myliobatiformes , Dasyatidae ) from China with mitogenomic evidence

Article References: Chen, J.-J., Chen, J.-Y., Guo, X.-L., Zeng, S., Yang, D.-Y., Zhong, J.-S., Zhao, S.-L., Fang, W.-H., Chen, J., & Liu, P. (2025). First records of Bathytoshia brevicaudata (Hutton, 1875) (Myliobatiformes, Dasyatidae) from China with mitogenomic evidence. Zoosystematics and Evolution, 101(4), 2191-2205. https://doi.org/10.3897/zse.101.164102

Image Credits: AI Generated

DOI: 10.3897/zse.101.164102

Keywords: Bathytoshia brevicaudata, short-tail stingray, East China Sea, China, mitogenome, marine biology, sexual dimorphism, trophic ecology, phylogenetics, elasmobranch conservation, First, records