Two kinds of cDNA fragments (KfhArr-R and KfhArr-C) encoding the putative arrestins of killifish, Oryzias latipes, were isolated. The distributions of these transcripts were investigated by in situ hybridization, and it was demonstrated that KfhArr-R and KfhArr-C are expressed in, respectively, rod and all four types of cone cells. The deduced amino acid sequences of KfhArr-R and KfhArr-C are closely related to human S-antigen (rod arrestin) and X-arrestin (cone arrestin), respectively. Phylogenetic analysis of arrestin sequences suggests that vertebrate visual arrestins form a single cluster distinct from other arrestins and diverged to form rod and cone subtypes before the divergence between teleosts and tetrapods. It is speculated that the divergence pattern of vertebrate visual arrestins may prove to be reflected in the divergence of the proteins participating in the respective phototransduction cascades.