Population ecology of landlocked ayu in Kasumigaura Lake system and its utilization and conservation

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Growth analysis using otolith microstructure, genetic analysis using microsatellite DNA, gut contents analysis and morphological comparison with different stocks were conducted on landlocked ayu population in Kasumigaura Lake system. Stable isotope analysis was also applied to estimate consumed food items. As a unique property of otolith microstructure, Kasumigaura ayu has transparent zone which lacks daily ring. Therefore it is difficult to determine hatched date from daily ring counts. We found daily increments of otolith correlated with water temperature and when increments decreased below 1mirco meter, transparent zone started to form. The formation of transparent zone lasted from middle January to late February. Estimated hached dates were distributed from late September to late November both for 2000 and 2001 samples. When hatched dates were compared between two samples taken from September to January and from February to April, difference was seen only for 2000 samples. As estim … More ated hatched dates were later for September to January sample in 2000, the survival of early hatched ayu juveniles was suggested to be low in 2000. The early growth of juveniles estimated based on backcalculation was well fitted for Gompertz growth curve. From the observation of stomach contents of juvenile ayu, prey items and size were altered at 2cm total length. This change was thought to be related with the shift of developmental stage occurring at 2cm total length. Microsatellite DNA analysis revealed that Kasumigaura Ayu differed from nearby amphidromous population at Pal5 locus. From stable isotope analysis carbon isotope values for within lake ayu were more depleted than upstream migrated ayu, and nitrogen isotope values were high for within lake fish, low for upstream migrated fish. This observation was well correspond to the observation that within lake ayu depend on zooplankton, but on attached algae for upstream migrated ayu. Gill raker length of Kasumigaura ayu caught in 1960s was long as same as nowadays Kasumigaura ayu. Less