BIOLOGICAL AND BIOCHEMICAL CHARACTERISTIC S OF YEARLING AYU IN THE OHTA RIVER OF HIROSHIMA PREFECTURE

Yearling ayu Plecoglossus altivelis collected in June and July from th e Ohta River were biologically and biochemically examined in compariso n with annual ayu caught in the same area. All the yearling ayu were f emale. The yearlng ayu were different in size and skin color from the annual ayu, but not different in anatomical parameters such as hepatos omatic index, intraperitoneal fat body ratio, and gonadosomatic index. The ovaries of annual ayu were immature and included chromatin nucleo lus and perinucleolus stage eggs, but those of yearling ayu consisted mostly of abortive eggs and a few chromatin nucleolus and perinucleolu s stage eggs. The yearling ayu had less muscle protein but more trigly cerides than annual ayu. Fatty acid composition of muscle triglyceride s in the yearling ayu was not different from that of the annual ayu. L ow protein accumulation caused by depression of protein metabolism wou ld affect the viability of yearling ayu after July.