Growth history and migration of the threespine stickleback Gasterosteus aculeatus in Otsuchi Bay, northeastern Japan

Both growth and migratory history of the Pacific Ocean forms of the threespine stickleback Gasterosteus aculeatus collected in Otsuchi Bay, northeastern Japan, were examined using otolith microstructure and analysis of strontium (Sr) and calcium (Ca) concentrations with wavelength dispersive X-ray spectrometry by an electron microprobe. Age of the juveniles (21.6-25.9 mm in total length) examined ranged from 101 to 128 days (115 +/- 8.5 days; mean +/- SD), hatching being estimated as having occurred between March and April 2001. The Sr: Ca ratios in the otoliths changed with both ontogenic development and salinity of the habitat. The otolith Sr: Ca ratios increased gradually from 4.1 x 10(-3) around the core to 7.5 x 10(-3) around the edge of the otolith. The fluctuation pattern of otolith Sr: Ca ratios was different from those observed in both freshwater resident and anadromous forms in previous studies. These results suggested that the fish sampled spend their lives in the estuarine and sea environment without freshwater life after hatching.