Reproductive isolation between sympatric Anguilla japonica and Anguilla marmorata.

Species-specific restriction fragment length polymorphism in the intron of the androgen receptor gene (ar5) was found in glass to silver-stage individuals of Anguilla japonica (n = 51) and A. marmorata (n = 21). The sequence analysis of 16S rDNA from 328 anguillid leptocephali collected in the North Equatorial Current of the western North Pacific Ocean revealed the specimens to be A. japonica (n = 194), A. marmorata (n = 128), A. bicolor pacifica (n = 5) and A. luzonensis (n = 1). All leptocephali of A. japonica and A. marmorata were monomorphic and did not share an allele at the ar5 locus, indicating that the two species are reproductively isolated.