Hakatajima Station, National Center for Stock Enhancement, Hakata, Ehime 794-2305, Japan
After their release into natural waters at a small inlet in the Seto Inland Sea, two groups of juvenile red sea bream, Pagrus major, reared under either low- or high-intensity light were studied to clarify changes in behavior and population size. Released fish showed two behaviors: aggregation and solitary. The low-intensity light group showed predominance over the high-intensity light group both in the number of solitary individuals and the spatial distribution area in the small inlet. Differences in these characters between the two rearing groups caused differences in the number of individuals able to win territories in the process of behavioral shift from aggregation to solitary type during 4-5 days after release.