Observations of Agonistic Behavior between Two Male Gobies Acentrogobius virgatulus (Jordan & Snyder, 1901), in Maizuru Bay, Kyoto Prefecture, Japan

Acentrogobius virgatulus (Jordan & Snyder, 1901) is a small coastal species of goby found along the Western Pacific. It is commonly found in Maizuru bay along the muddy sediment between the intertidal zone and depths of 10 m. In June and July of 2022, two independent agonistic interactions between male A. virgatulus were observed and recorded during its spawning season. One interaction, lasting over 4 minutes, included certain aggressive behaviors such as jaw locking, mouth gaping, fin extensions, rapid color changes, and fast strikes to the head and body. Another interaction exhibited similar mouth gaping, fin extension, and rapid color changes but did not lead to further escalation. These behaviors coincide with those found in similar species and provides in situ evidence of these uncommon interactions. This is the first record of agonistic behavior by an Acentrogobius species. Accumulating findings such as these can contextualize intraspecific interactions, reveal differences across multiple species, and guide future experiments.