Abstract
In this study, we investigated mating system and mate choice of the triplefin blenny Enneapterygius etheostoma on a rocky reef at Banda, Tateyama Bay, Chiba, Japan, from 21 May to 19 July 2020. The larger males maintained a territory, while the smaller ones joined reproduction as a sneaker. The females visited the territorial males to spawn. The mating success of each territorial male was evaluated by the number of females they spawned with, and eight morphological traits were measured and analyzed to investigate the factors to determine their mating success. There was a significant difference in mating success among the territorial males. However, it was suggested that females choose males regardless of morphological traits and did not always choose the same males. The mating success of territorial males may be determined by chance or mate-choice copying by females.