Females of a stream goby choose mates that court in fast water currents

Males of the stream goby Rhinogobius sp. DA with exclusive paternal care co urt females in fast water currents. Female choice of this goby was observed in the field. A fast current itself does not seem to be advantageous to fe males for mating. Neither large male size nor long male dorsal fin, both be ing sexually dimorphic traits, was related to female selectivity. Females f avored males that courted on points at which the water current was relative ly fast. Water velocity at male courtship points was positively correlated with a condition factor for males, indicating that males of poor physical c ondition do not court in fast water currents. Hence, this mate choice patte rn enables females to mate with males of good physical condition. Male cond ition factor itself, however, was not related to selectivity by females. Ci rcumstantial evidence suggest that this female choice pattern will result i n mating with males having sufficient energy reserves, i.e. high parental q uality.