New Genetic Discoveries in the Freshwater Fish“Pike Gudgeon”! Two New Species to be Named

Public Relations Office        May 30, 2017

Koji Tominaga, Kwansei Gakuin Senior High School Teacher (science)

Koji Tominaga, Kwansei Gakuin Senior High School Teacher (science)

Born 1984. Graduated from Kwansei Gakuin Senior High School in 2003 and from the Bioscience Department of Kwansei Gakuin University’s Faculty of Science and Technology in 2007. Completed the first half of the Doctoral Program in the Division of Biological Sciences of Kyoto University Graduate School of Science in 2009. Left the second half of the Doctoral Program in 2011 and took up his current position in the same year. Areas of specialization are molecular phylogeny, biogeography, evolutionary biology, and phylogenetic systematics.

Koji Tominaga, a teacher at Kwansei Gakuin Senior High School, has investigated the freshwater fish, Pseudogobio esocinus (pike gudgeon), and, in a Japan first, discovered that, while this species was previously believed to consist of a single group, genetically, it actually consists of three different groups on a species level. The following is a description of his research, which was published in Ichthyological Research, the Englishlanguage journal of The Ichthyological Society of Japan in July 2015.

The pike gudgeon is a freshwater fish of the cyprinid family, about 20 cm in length, found in rivers throughout Japan, with the exception of Hokkaido and Okinawa. For the research, approximately 1,200 individual specimens were collected from 200 locations throughout the Pseudogobio esocinus distribution area. Differences in the base sequences of DNA isolated from the fins of the individuals were examined, and a phylogeny showing the phylogenetic relationship of the individuals on dendritic lines was constructed. The researchers found that there were three differentiated groups or “clades”, A, B, and C, whose genes differed at a species level. They also found that two of those groups, Clades A and B, were distributed in western Japan, while Clade C was distributed in eastern Japan.

The phylogeny (Fig. 1) shows a timeline from 10 million years ago to the present. The degree of genetic differentiation was used to estimate when each groups and local populations diverged. For example, clade A had diverged from the continental lineage around 5 million years ago and clade B and C around 8 million years ago.

The transition of geographic distribution (Fig. 2) was analyzed using geological data. It was surmised that the three clades have not hybridized since ancient times, when the Japanese archipelago was still connected to the mainland, and that their distribution areas expanded at mutually different times.

(Fig. 1),(Fig. 2)

Freshwater Fish“Pike Gudgeon”

The next step is to present objective data on the differences between the newly discovered P. esocinus clades, such as shape and coloration, and to report them as new species of freshwater fish in a published paper. This will overturn the common wisdom held since the discovery of P. esocinus in the 19th century, namely that there is only one species of Japanese pike gudgeon. The data has already been collected, and Mr. Tominaga is in the process of writing the paper to present these further findings. “One of the three clades is the ‘true’ P.esocinus that has already been documented. The other two clades are completely new, unknown species. I am currently thinking about what
scientific names and Japanese names for the new species that I will propose in my paper.” Mr. Tominaga’s enthusiasm for this task is obvious. He already has some candidates for the nomenclature, which he will announce at the same time that his paper is published. “Ultimately, I want to use my research into P. esocinus to shed light on the mechanisms of fish speciation.”

Mr. Tominaga has loved fish since he was a child. As a student at Kwansei Gakuin Senior High School, he conducted his own, independent research, and published a book on his observations of freshwater fish, Visiting Japan’s Freshwater Fish – An Examination of Rivers and Fish [Nihon no Tansuigyo wo Tazunete – Kawa to Sakana wo Yomu]. Noticing the slight variations in the appearance of the P. esocinus that he observed at that time, he developed a hypothesis that cryptic species of P. esocinus must surely exist. Subsequently, he studied molecular biology, at Kwansei Gakuin University’s School of Science and Technology before moving on to the Graduate School of Kyoto University. There, he immersed himself in his research into P. esocinus, traveling to rivers throughout the country. Today, as the advisor for Kwansei Gakuin Senior High School’s after-school science club, he accompanies students on field trips to rivers, where he is continuing his field research. Smiling, he said, “It is precisely because I am a high school teacher that I want to interact directly with the students and convey to them my own experience and knowledge. I also want to be a good role model as a researcher in the field of biology.”