Understanding the mechanisms behind the coexistence of ecologically similar species is a key challenge in biodiversity research, and closely related species with overlapping distributions are often a focus for such studies. Gobiidae is the most diversified family in marine fish taxa, being well adapted to various environments in coastal areas. In this study, we focused on three sympatrically occurring gobies (Acentrogobius sp. A, B, C), which had been recognized as one species “A. pflaumii” until recently due to their similarity and aimed (1) to describe their geographic distribution and (2) to clarify their habitat segregation across the Japanese archipelago.

Exhaustive specimen sampling along the Japanese archipelago (345 sites) revealed that the distributions of the three species broadly overlap although both the northern and southern distribution ends of sp. A are located at lower latitudes. Two environmental factors (water depth and salinity) were significantly different among species; Sp. A was found in shallow waters with a wide range of salinities, whereas sp. B was found in moderate depths with high salinities and sp. C in the deepest and highest salinity areas. This tendency is common throughout Japan, suggesting that segregation in habitat enables the three species to coexist across their distributional range.