Predation by fishes on released seedlings of the Japanese mitten crab Eriocheir japonica

Abstract

Predation on released seedlings of the Japanese mitten crab, Eriocheirjaponica, by fishes was examined in the upper reach of the Koya River and middle reach of the Nishiki River. Stomach contents of fishes sampled before and after the release in the upper and middle reaches, were analysed. Mortality of crabs caused by fish predation was high in the upper reach, but lower in the middle reach. This difference is suggested to be largely due to differences in the diversity of potential prey species for the fishes at the two study sites. In the upper reach with a low diversity of prey species, the released juveniles had high a prey value to fishes and subsequently, fishes fed heavily on them.