Life History Characteristics of a Sicydiinae Goby in Japan, Compared with Its Relatives and Other Amphidromous Fishes
Midori Iida, Shun Watanabe, and Katsumi Tsukamoto
Abstract—Sicyopterus japonicus is unique because it is the only temperate amphidromous goby of the subfamily Sicydiinae. Life history and migration characteristics of S. japonicus, including seasonal changes of condition factor, spawning season, hatching size, oceanic larval duration, recruitment season, and size at recruitment, were examined in the temperate region of western Japan and were compared with those of other Sicydiinae species, all of which inhabit the tropics and subtropics. The condition factor varied seasonally, with peaks in July and November. The spawning season of S. japonicus ranged from July to September, with a peak in July–August, and was shorter than that of other species that normally spawn from 7 to 12 months/year. The hatching size (1.5 mm total length) was similar to other Sicydiinae, but oceanic larval duration (range: 173–253 d) was longer than most other species. The long larval duration and single annual reproduction period suggest that it is adapted to longdistance oceanic dispersal. The recruitment season (about 4 months) is the shortest known among the Sicydiinae, but its size at river entry (mean: 26.3 mm standard length) was similar to other species. The shorter reproductive and recruitment seasons for S. japonicus probably indicate that its migration strategy is determined by seasonal changes in the temperate region. Sicydiinae species have larger clutch sizes and smaller hatching sizes compared to other temperate amphidromous families such as the Galaxiidae, Osmeridae, and Cottidae. Sicydiinae species have no nondiadromous forms, suggesting that they may have a migration strategy with a high oceanic dependency that facilitates oceanic dispersion.