Dietary preferences of the Japanese mitten crab Eriocheir japonica in a river and adjacent seacoast in north Kyushu, Japan

The diet of the Japanese mitten crab Eriocheir japonica was investigated by examining the stomach contents of middleand large-sized crabs (carapace width 10 mm). Crabs were collected in the freshwater area (growth area), tidal river, and seacoast area (reproductive area) of the Saigo River, Fukuoka Prefecture, Japan. Analysis of the diet of E. japonica was carried out using the frequency of occurrence and percentage point methods. The stomach contents were classified into 4 large and 27 small categories. It was evident that E. japonica was an omnivore and a deposit feeder, mainly feeding on the detritus derived from vascular plants growing along the river channel. Filamentous algae Cladophora sp., aquatic insects (e.g., Chironomidae), sediments such as mud or sand, and artificial products such as plastic or yarn were often found, suggesting that E. japonica mainly feeds on detritus lying on the substrate without sorting well. Stomach contents of adult crabs in the tidal area exhibited higher frequency of animal materials (i.e., fish, gastropods, and crabs) than those of young and adult crabs in the freshwater area, suggesting that adult crabs in the tidal area eat more animal materials. Such an omnivorous feeding habit is similar to other related brachyuran crabs (grapsoidae) and may be one of the important factors which enables E. japonica’s wide distribution along the river and sea-