MATURATION AND AGE IN DAYS OF PACIFIC SAU RY COLOLABIS-SAIRA (BREVOORT) IN THE CENTRAL NORTH PACIFIC-OCEAN DURING THE SUMMER

The maturation process and age in days of female Pacific saury Cololab is saira (Brevoort) in the central North Pacific Ocean were examined b ased on histological observations and otolith daily growth increments. The maturation process of Pacific saury used in this study (243-342 m m in knob length) was divided into 6 stages: early yolk vesicle stage, late yolk vesicle stage, yolk formation stage, maturation stage, atre tic stage I, and atretic stage II. Atretic stage fish were considered to be post-spawning as many degenerated oocytes were observed. The lar ge size group (more than 296 mm), in which fish were more than 1.5 yea rs old as estimated from daily growth increments in otoliths, containe d spawning and post-spawning individuals, although all individuals fro m the medium size group (241-295 mm), from 10 months to 1 year and 3 m onths old, were immature. Since post-spawning fish were seen to have r ecovered their initial condition factors, it is suggested that they su rvive beyond the first spawning season. Based on observations of async hronously developing oocytes, it is considered that Pacific saury spaw n several times during a single spawning season.