The three species of amphidromous gobies (Rhinogobius sp.CB, CO and LD) allopatric in the Aizu River, Wakayama Prefecture, Japan were examined for their clutch size and egg size. Clutch size was the largest in R. sp.CO and the smallest in R. sp.CB, whereas egg size was in the reverse order. Larger clutch size in R. sp.CO and LD than R. sp.CB was partly explained by the difference in body size, because the formar two species have a larger body size at maturation than the latter. The differences in reproductive characteristics may be a result of the different survival rates of larvae during migration to the sea, because their spawning ground distributions are different from one another along the stream.
