Females prefer males with larger first dorsal fins in the common freshwater goby

Males of the common freshwater goby Rhinogobius brunneus , which provide paternal care, have a first dorsal fin (FDF) that is markedly longer and more elaborate in colour and shape than that of females. Females showed a clear preference for males with longer FDFs, but mated randomly with respect to male body size ( L _s) and nest size. They were individually consistent in their choice of mates, and the strength of preference increased with inter-male differences in FDF length. During courtship, despite the unequivocal preference, females seem not to rely on FDF size in choosing a mate, but the leading display of males appears to play an important role in female choice. The results of this study suggest that intersexual selection probably contributes to the evolution of the elaborate FDF.