Abstract: Light intensity as one of the most important environmental parameters has been shown to significantly influence growth and survival of larval or juvenile fish. The juvenile (with body weight of 10.10-+ 0.8g) masu salmon Oncorhynchus masou masou were reared in polyethylene tanks (80 cm diameter, 60 cm tank depth with water level of 40 cm) with a flowing freshwater at light intensity of 1200 lx, 600 lx, and 300 lx)at ambient temperature of 12.1 - 13.9℃ for 50 days to evaluate the effects of light intensity on growth performance. The light intensity was found to influence specific growth rate(SGR ), condition factor(CF) and coefficient variation (CV) significantly (P〈 0.01 ). The juveniles reared in high light intensity ( 1200 lx) had significantly higher SGR and CF than the juveniles reared under light intensity of 600 lx and 300 lx did. However, there was the lower CV under 1200 lx than under the other two light regimes. Correspondingly, the juveniles reared in high light intensity ( 1200 lx) showed significantly higher feeding intake compared to the animals under light intensity of 600 lx and 300 lx, indicating that increasing light intensity led to the positive effects for the growth in the juveniles. These findings contribute valuable information to the continuing development of juvenile culture of the juvenile masu salmon.

Key words: Oncorhynchus masou masou, light intensity, growth performance, feeding intake