Nagasaki University clarifies the familiar red stingray is "actually multiple species"

The red stingray, well known as one of the most familiar rays along Japan's coasts, is actually multiple species that have been mistakenly thought to be a single species for over 160 years, which was revealed by a research team led by Professor Atsuko Yamaguchi and Researcher Keisuke Furumitsu at Nagasaki University. Through this research, they have redescribed the species conventionally known as the red stingray, " Hemitrygon akajei," and described the cryptic species known as the Ariake stingray, first discovered in the Ariake Sea, as the new species " Hemitrygon ariakensis." Their findings were published in the early online edition of Ichthyological Research.

During the Edo period, the red stingray was collected from various locations across Japan by Philipp Franz von Siebold and his associates and sent to the Dutch National Museum of Natural History (now the Naturalis Biodiversity Center). Based on six specimens, it was described as a new species by Johannes Müller and Jakob Henle in 1841. Because all six specimens were very similar, they were believed to be the same species.

Subsequently, research at Nagasaki University has revealed that there are multiple species of Hemitrygon stingrays in the Ariake Sea that are so similar in appearance they are difficult to distinguish. Additionally, close examination of the illustrations in the paper described by Müller and Henle showed a different appearance from the red stingray, raising a question as to whether H. akajei was actually the red stingray.

To resolve this question, the research team has been conducting taxonomic research on red stingrays since 2003. After revealing the existence of a cryptic species in 2010, they formally described it as a new species with an official scientific name through 15 years of investigation, research, and examination of historical materials.

It had been believed that the six type specimens from the year 1841, when H. akajei was described, were housed at the Naturalis Biodiversity Center in Leiden. However, in the mid-20th century, an investigation by Dutch researcher Boeseman revealed that there were actually seven specimens in total, with one specimen having been added, and all of these were provisionally considered to be H. akajei. At that time, the specimen collected by Siebold in Nagasaki was designated as the lectotype.

When Yamaguchi's research team actually examined the seven specimens, they found that multiple species were mixed among them, and that the original description had conflated the characteristics of multiple species. Furthermore, the research was extremely difficult because the lectotype was a juvenile that did not fully exhibit morphological characteristics.

Therefore, they collected many juveniles of red stingray species (red stingray, Yantai stingray, Izu stingray, etc.) and conducted taxonomic comparative studies. As a result, they found that the lectotype of H. akajei and the ray currently called the red stingray were the same species. If the Ariake stingray had been designated as the lectotype, the Japanese name and scientific name could have been reversed. In response to this finding, they conducted a redescription of H. akajei, including variations due to growth stages and sexual differences, to clarify its characteristics once again.

During the research process, it became clear that there is another ray, mainly present in the Ariake Sea, so similar to the red stingray that they are indistinguishable. After morphological and genetic research, the Japanese name "Ariake stingray" was given to this ray in 2010, but the scientific name remained undetermined. As a result of further examination, the Ariake stingray was revealed to be a new species, and it was described as a new species with the scientific name H. ariakensis. An individual collected off Shimabara (Nagasaki Prefecture) in the Ariake Sea was designated as the holotype. Furthermore, surveys that clearly distinguish between the red stingray and the Ariake stingray are revealing that there are differences in the ecology of both species.

Moreover, close examination of The Fishes of Southern and Western Japan (commonly known as the Glover Atlas), which was created from the late Meiji period onward and is housed in the Nagasaki University Library, revealed that the only illustration drawn as the red stingray was actually the Ariake stingray.

With the revelation that the red stingray, which had been lumped together as a single species, is actually multiple species, it becomes possible to accurately assess the ecology, distribution, and resource levels of each species.

Journal Information
Publication: Ichthyological Research
Title: Redescription of Hemitrygon akajei with description of the cryptic stingray species Hemitrygon ariakensis sp. nov. from the Northwest Pacific (Myliobatoidei: Dasyatidae)
DOI: 10.1007/s10228-025-01048-5