Migratory pattern and larval duration of an amphidromous goby (Rhinogobius nagoyae) at Sado Island, in northern Japan

The larval period is a critical stage for many aquatic organisms, because larvae are small, fragile, and have high mortality rates. Amphidromous fish spend their larval stages in the sea, and larval durations vary, possibly reflecting their dispersal tendencies. The genus Rhinogobius (suborder Gobioidei) is widely distributed throughout Asia and exhibits a variety of migratory patterns. Despite some studies of their migratory histories, larval durations of Rhinogobius species are uncertain. This study used analyses of otolith microstructure and trace-elemental chemistry to investigate habitat use throughout the life history of R. nagoyae. Twenty-six adult gobies were collected from seven rivers on Sado Island, in northern Japan, and otolith Sr:Ca ratios were quantified using electron microprobe analysis to infer amphidromous movement. All individuals showed shifts in Sr:Ca ratio across the otolith transect, which indicated movement between freshwater and saltwater. Marine larval duration was estimated by otolith increment counting, combined with Sr:Ca ratio. Larval duration ranged from 29 to 45 days (mean, 35.3), and there were no significant differences among rivers on the island. The relatively short larval duration of R. nagoyae, compared with other amphidromous fish such as ayu and galaxids, may reflect environmental factors such as island size, cool weather or species characteristics.