山梨県西湖及び精進湖におけるオオクチバスの食性

抄録

Using an index of relative importance (IRI), we studied the feeding habits of non-indigenous largemouth bass, Micropterus salmoides, in two lakes, Lake Saiko and Lake Shojiko, Yamanashi Prefecture, Central Japan. In Lake Saiko (n = 64), fishes, particularly a species of goby (Tridentiger brevispinis), were the main prey of bass (%IRI = 77.6%). In Lake Shojiko (n = 134), bass predated both fishes (%IRI = 46.6%) and crustaceans (%IRI = 49.5%), and the main prey species were another goby (Rhinogobius spp.) and a prawn (Macrobrachium nipponense). It appears that bass prey on any species that are available. Furthermore, prey selection differed according to the body size of the bass in one lake, but not in the other. In Lake Shojiko, individuals with a body length (BL) greater than 200 mm mainly predated crustaceans, whereas bass with a BL less than 200 mm mainly consumed fishes. In contrast, regardless of their body size, bass in Lake Saiko mainly preyed on fish. It appears that food selection by bass in these two lakes, which are in close proximity, is related to the availability and size distribution of the main prey species.