The mottled spinefoot Siganus fuscescens, one of representative consumers associated with deforestation of temperate seaweed beds in Japan, is nominally herbivorous fish. However, it is noted that the mottled spinefoot favors animal matters such as forzen krill and fish in the rearing tank in relation to its trophic position and overbrowsing of overstory macroalgae. This study examined feeding pattern of animal matter (frozen krill) and fucoid algae or kelp forming seaweed beds by the mottled spinefoot in an indoor tank with the aid of artificial food uniforming different accessibility and/or texture of prey items using sodium alginate gel. In a feeding experiment with artificial foods of mixture of krill and fucoid alga turned into fluid with a blender, krill 100% food was predominantly consumed, but fucoid alga 100% food (krill 0%) was also consumed as much as or more than krill 20-80% mixture foods. A two-choice feeding experiment of unlimited supply of artificial foods of no processing krill or fucoid alga was conducted for 6 hours and artificial food of fucoid alga was also consumed constantly as well as that of krill, not based on individual variability of fish feeding. Utilization of animal matters and algae is discussed in relation to morphological features of herbivorous fishes and distributional dynamics and nutirional values of prey resources.