Abstract
Poor growth phenomenon of Sargassum fusifoyme thought to be caused by fish feeding has been occurred recently along the coastal region of Nagasaki Prefecture. We conducted feeding experiments on S. fusiforme in outdoor tanks with six herbivorous fish species that occur in the study area. Three species, Siganus fuscescens, Kyphosus bigibbus, and Calotomus japonicus fed on S. fusiforme in significantly and left characteristic bite marks on the thalli: bite marks are regular and smaller serrated scars by S. fuscescens, slightly irregular and wider serrated scars by K. bigibbus, and irregular rugged scars by C. japonicus. Of these three species, S. fuscescens fed 15 to 20 times more on S. fusifoyme than the two other species and showed feeding selectivity. On S. fusifoyme collected from the site where poor growth typically occurs, 39 to 67% of the specimens had characteristic bite marks made by S. fuscescens. This suggests that the species that cause poor growth through feeding can be identified from observations of the bite marks, and S. fuscescens is probably the most influential species at this site.
