TSUKAMOTO Yoichi Ocean Research Institute, The University of Tokyo Researcher, 海洋研究所, 農学特定研究員
OTAKE Tuguo Faculty of Bio-resources, Mie Univ., Associate Professor, 生物資源学部, 助教授 (20160525)
Shirasu larvae in clupeid, engraulid, plecoglossid, ammodytid fishes are characterized by elongated body and poor melanophore development. These fished constitute major fish resources whose population usually fluctuate greatly. Growth history in the larval and juvenile stages is considered to be a major factor controlling population fluctuation. Otolith daily growth rings are now used for analyzing growth history of individual fish. in Ammodytes personatus, fine growth rings less than 1 mum in width between neighboring rings were found under scanning electron microscope. In Sardinops melanostictus, fine rings were found in otolith area where distinct daily rings were not visible under a light microscope.
Sr : Ca ratio of otolith were found to be a effective tool for reconstructing migration history in Plecoglossus altivelis to discriminate amphidromous population from non-amphidromous one. In Sardinops melanostictus, however, otoith Sr : Ca did not change in parallel with temperature or salinity fluctuation and cannot be used as a tool of life history analysis.
Growth history analyses based on otolith daily growth rings revealed that somatic growth rates in Engraulis japonicus declined from the coastal to offshore waters off the Thhoku region in the northwestern Pacific. In Sardinops melanostictus, the cohorts migrated north to the Kuroshio-Oyashio transition waters were comparatively uniform in growth history, while variable growth histories were found in the cohorts migrated to the Pacific coastal waters off central Japan. The cohorts migrating north may be uniformly affected by variable environments in the Kuroshio-Oyashio transition waters and suffer from great fluctuations in recruitment.