Abstract
Fighting for a shelter between Palaemon pacificus and P.serrifer were investigated in aquaria. In both interspecific and intraspecific fighting,the smaller individuals were usually eliminated by the larger ones from the shelter. In the case that smaller individual was a winner, P. serrifer won more often than P. pacificus although P. serrifer was smaller. The second pereiopod was longer in P. serrifer than in P. pacificus. P. serrifer made up for smaller body size by larger second pereiopod length than P. pacificus relatively.
