Abstract
Seasonal changes in gonadosomatic index, hepatosomatic index, condition factor, and stomach content index of samples collected by experimental trawls from November 1981 to February 1985 were examined to clarify the annual life cycle and distribution of adult Pleuro-nectes herzensteini in the coastal waters of northern Niigata Prefecture. In addition, 1, 126 tagged fish were released in the autumn of 1984. Adult fish were concentrated in the offshore area at a depth of more than 130 m from August to December. From January to February, they migrated toward the inshore area (50-90 m) from Niigata Prefecture to Toyama Prefecture as gonads developed and they spawned between February and May. Migration toward the offshore area occurred chiefly after June. Feeding intensity expressed as stomach content index increased after the spawning season and decreased after August-September when hepatosomatic index and condition factor attained a peak in the seasonal cycle. From these results, the annual life pattern of adult P. herzensteini is roughly divided into the following four periods; spawning migration (January-February), spawning (February-May), active feeding and feediing migration (May-July), and inactive feeding (August-December).
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