Growth and expansion of habitat of released nigorobuna Carassius auratus grandoculis juveniles in Lake Biwa, and effective release strategies to the offing

Abstract

Reed zones indispensable for the development and early growth of nigorobuna Carassius auratus grandoculis in Lake Biwa are on the decline. In order to examine eŠective release strategies for thisˆsh independent of reed zone, a follow-up survey of otolith marked juvenile nigorobuna with ALC released into reed zones in June to July was conducted. As a result, growth of nigorobuna was as good as in the year with high water temperature from August to October. Nigorobuna extended the distribution along with the thermocline when the water temperature fell gradually toward winter, and expanded the distribution toward the bottom of the lake when the water temperature diŠerence of the upper and lower layers of the thermocline was less than about 3.5 degrees. High survival was expected by releasing young nigorobuna of body weight ca. 20 g (standard length ca. 85 mm) to the o‹ng during this period.