Nest-use pattern of fluvial goby (Rhinogobius flumineus) in relation to the presence or absence of amphidromous congener: a case study of two rivers in southern central Honshu, Japan

Abstract

Fishes of the genus Rhinogobius (Gobiidae) display paternal care of their nests, constructed beneath stones. Rhinogobius flumineus often coexist with larger Rhinogobius congeners (hence, stronger competitors for the nest site). To understand how R. flumineus reproduce successfully with the presence of a potential nest site competitor, nest-use characteristics of R. flumineus and Rhinogobius nagoyae were investigated in two rivers in southern central Honshu, Japan: one site with both species in sympatry and the other site with R. flumineus in allopatry. Analyses of nest stone, egg clutch, and male body sizes demonstrated that reproductive success, namely the number of eggs deposited, increased with male body size in both species and was positively correlated with nest stone size only in R. nagoyae. The pattern that R. flumineus males are less insistent on using large stones for nesting may partly explain the coexistence mechanism of the two species.