The contents of stomach and intestines of specimens of Siganus fuscescens from Futaoi Island in the Sea of Hibiki were analysed and the percentages of each algal species and animal taxanomic groups were determined. 64 specimens, ranging from 168 to 312 mm body length, were collected by bottom gill net and commercial trap net in autumn (September and October) of 1998 and late spring (May) of 1999. The diet of S. fuscescens consisted dominantly of laminarian and fucoid algae, with an animal component of less than 2% by wet weight. The degrees of similarity and diversity, on a weight basis, in the diet of S. fuscescens were compared between autumn and Spring. The dietary composition in spring was greatly different from that in autumn, and two annual species of undaria pinnatifida and Sargasstm horneri overwhelmingly dominated in spring, whereas diverse perennial species of laminarian and fucoid algae constituted the diet in autumn. There was evidence of selection of reproductive receptacles of fucoid algae as an important food source. These results emphasize the unusual feeding pattem of adult S. fuscescens among the members of the family Siganidae.
