Members of the genus Rhinogobius are widely distributed in Far East Asia, at least 11 species having been recognized in Japan. Of the six species recorded from Okinawa Island, two are land-locked (“aobara-yoshinobori” R. sp.BB and “kibara-yoshinobori” R. sp.YB) and the remainder amphidromous. Embryonic development and morphological changes in the two land-locked species are described from artifically-reared eggs, larvae and juveniles. Survival and growth of the two species were compared under different salinities (0-35%0) dur-ing a 21-day period following hatching. Although egg diameters of both species were almost the same (“aobara-yoshinobori”; 4.3±0.1 mm, “kibara-yoshinobori”; 4.3±0.2 mm), newly-hatched larval morphology, and larval and juvenile salinity tolerance clearly differed. Newly-hatched larvae of “aobara-yoshinobori” had a flexed notochord and caudal fin rays already developed. The yolk was completely consumed 3 days after hatching. By comparison, “kibara-yoshinobori” hatched at an ealier developmental stage, having a straight notochord. The yolk disappeared 7 days after hatching. Larvae and juveniles of “aobara-yoshinobori” were less toler-ant in high salinity than those of “kibara-yoshinobori”. The results suggested that the two land-locked gobies have become adapted to a wholly fluvial life cycle, through somewhat different strategies.
