SOME ASPECTS OF THE BIOLOGY OF BATHYLAGUS-OCHOTENSIS (PISCES, BATHYLAGIDAE) IN SAGAMI BAY, CENTRAL JAPAN

Vertical distribution, seasonal occurrence and growth of larval and ju venile (<50 mm standard length [SL]) Bathylagus ochotensis were invest igated utilizing discrete-depth and monthly oblique-haul samples at a fixed station in Sagami Bay, central Japan. Unlike other midwater fish es, the larvae did not occur in the upper 200-m layer, remaining in th e upper mesopelagic zone (ca. 300-600 m) during both day and night. Th ey exhibited a clear size-depth stratification within the latter depth range, larger individuals occurring deeper. Seasonality in occurrence was evident; larvae being recorded from October to May, with abundanc es peaking in January and February. Modal progressions in monthly leng th-frequency distributions indicated that B. ochotensis metamorphoses at around 18 mm SL, about 3 months from hatching, and attains 34 mm SL after 1 year, at which time all individuals are juveniles. Extrapolat ion of growth curves, supplemented by observations on adult specimens, suggested that males and females attain sexual maturity after 3 and 4 years (at about 70 and 100 mm SL), respectively.