Intraspecific diversity of fan-tailed brook lamprey (Lethenteron satoi) with its ecological and distributional notes

Lethenteron satoi is a species of brook lamprey recently described from a single river in the Ishikari River system, Hokkaido, Japan. To date, the species had been known only from the six specimens used in the original description, and its basic biological information remained extremely limited. Herein, we examined genetic and morphological variation in L. satoi based on 38 individuals collected from four rivers. Mitochondrial DNA analyses revealed that genetic diversity is highest in the lowland areas of the Ishikari River system and that populations are genetically differentiated from one another. Morphological analyses showed that a population from the upper reaches exhibits partially distinct characters and allow us to update the known ranges of metric traits for the species. We also provide new information on the distribution, ecology, and sexual dimorphisms of L. satoi . These findings provide a foundation for future conservation of this recently described species.