1Shiga Prefecture Fisheries Experiment Station, Hikone, Shiga 522-0057, 2Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan
Changes in swimming speed of larval and juvenile nigorobuna Carassius auratus grandoculis associated with its growth and exercise training in running water were investigated in order to obtain basic data for considering the effective release strategies for the stock enhancement program in Lake Biwa. As a result, increase in burst speed was observed until approximately 16 mm in standard length (SL). During the juvenile stage (≧16 mm SL), a rapid increase in the cruising speed and a marked increase in the swimming ability were observed. The results strongly indicate that ca. 16 mm SL is an effective criterion for release. Increase of burst speed in larval and/or juvenile nigorobuna by exercise training in running water was observed, but when the fish reared in running water and still water were released in concrete ponds with one or two largemouth bass Micropterus salmoides as a predator and in the natural environment of Lake Biwa, significant differences were not recognized in the survival rates between trained and still water reared fish.