Discovery of two new lamprey species: Five species of the genus Lethenteron in Japan reported by National Fisheries University and other institutions

A research group including Professor Emeritus Harumi Sakai of the National Fisheries University, Japan Fisheries Research and Education Agency, Professor Emeritus Akihisa Iwata of the Graduate School of Asian and African Area Studies and Professor Katsutoshi Watanabe of the Graduate School of Science at Kyoto University and Former Professor Akira Goto of the Department of International and Regional Education at Hokkaido University of Education re-examined genetic and morphological aspects of Japanese brook lampreys of the genus Lethenteron, which has been subject to considerable taxonomic confusion. They have reported two new lamprey species, Uchiwa-sunayatsume (English name "fan-tailed brook lamprey" Lethenteron satoi) and Minami-sunayatsume (English name "southern Japanese brook lamprey", Lethenteron hattai), and revealed the existence of five species in total, including Kita-sunayatsume (English name "northern Japanese brook lamprey", Lethenteron mitsukurii), Shiberia-yatsume (English name "Siberian lamprey", Lethenteron reissneri), Kawa-yatsume (English name "Arctic lamprey", Lethenteron camtschaticum), and the two new species. The study was published online in Ichthyological Research of the Ichthyological Society of Japan.

There has been considerable confusion regarding the classification of lampreys of the genus Lethenteron in Japan since the early twentieth century. Traditionally, three species were considered to inhabit the country: Arctic lamprey (Lethenteron camtschaticum), Japanese brook lamprey (former Lethenteron reissneri), and Siberian brook lamprey (former Lethenteron kesslreri). Recently, the existence of two cryptic species within Japanese brook lamprey (former Lethenteron reissneri), referred to as the northern and southern types, has been revealed using genetic techniques. However, because species in this group are very similar with each other, researchers could not find any distinguishing features for each species and could not assign scientific names.

To determine the discernible features of each species, the research group focused on adult fish that had fully matured after metamorphosis and had the most developed morphological characteristics and re-examined the morphological characteristics of genetically classified groups based on DNA sequences. Consequently, in addition to the two previously known cryptic species (northern and southern species) of Japanese brook lamprey (former Lethenteron reissneri), Siberian lamprey (former Lethenteron kessleri), and Arctic lamprey (Lethenteron camtschaticum), another unknown species was discovered in Japan, showing that a total of five Lethenteron species inhabit Japan. As they could find the discernible features of each species through detailed morphological observation, they described the newly discovered unknown species as a new species, Lethenteron satoi (Japanese romaji name: Uchiwa-sunayatsume), and southern Lethenteron species as a new species, Lethenteron hattai (Japanese romaji name: Minami-sunayatsume). Moreover, they established the scientific name for northern Lethenteron species as Lethenteron mitsukurii (Japanese romaji name: Kita-sunayatsume) and redescribed this species. Indeed, the scientific names of Minami-sunayatsume (Lethenteron hattai) and Kita-sunayatsume (Lethenteron mitsukurii) have been determined 28 years after their discovery.

The research group commented on the findings: "The lamprey fishes of the genus Lethenteron are a group that is feared to be unknowingly extinct, but there has been significant taxonomic confusion and conservation targets have remained unclear. Thus, those who had been and had not been involved in lamprey research up until now reached out to each other and worked together, making use of each other's strengths, to try to resolve the problem. Although it took a long time, we were able to find diagnostic morphological features, which caused the confusion. Moreover, we unexpectedly discovered a new species that was completely unknown to us. We are very happy to finally be able to publish this paper and feel a great sense of accomplishment. We hope that the lampreys, inconspicuous "river dwellers" since old times, will continue to live in a healthy manner forever."

Journal Information
Publication: Ichthyological Research
Title: Taxonomic re-examination of Japanese brook lampreys of the genus Lethenteron with descriptions of two new species, Lethenteron satoi sp. nov. and Lethenteron hattai sp. nov., and re-description of Lethenteron mitsukurii
DOI: 10.1007/s10228-024-00997-7