The microhabitat and size of gammarid species selectively predated by young red sea bream Pagrus major

Mechanisms of prey selection by young red sea bream Pagrus major were examined in Shijiki Bay by comparing the species composition of gammaridean amphipods in the diet with that in the environment. Although gammarids were the major source of food for young red sea bream, their species composition in fish stomachs changed with the growth of fish from June to October and always differed from that in the environment. The patterns of selection of gammarids were related most closely to the microhabitat of each species before mid-July. The order of selectivity of species in terms of the microhabitat was as follows: epifaunal species > shallow-burrowing species > infaunal tube-dwelling species > deep-burrowing species. After mid-July, however, selection was determined by the body size of gammarid species. Byblis japonicus that were large enough as a prey species were mainly consumed and other smaller species were not selectively eaten. Thus, the microhabitat and the body size of gammarids play dominant roles in prey selection by young red sea bream.