Growth of the bivalve-feeder Halla okudai (Polychaeta : Lysaretidae) underwild and rearing conditions, in relation to species and abundance of prey organisms

Growth of the bivalve-feeder Halla okudai (Polychaeta: Lysaretidae) was eva luated in relation to species and abundance of prey under wild and rearing conditions. The field survey was conducted from May to July 1995 at the M.L .W.S. in II intertidal sandy flats of Hiroshima Bay, the Seto Inland Sea. H . okudai habitats were classified into four types by major prey organisms: clam, clam & oyster, oyster, and mussel. The condition factor was highest i n the clam & oyster-type habitat with the highest density of Ruditapes phil ippinarum. The condition factor also increased with increasing the density of R. philippinarum, whereas this was not seen in Crassostrea gigas and Myt ilus galloprovinciallis. In laboratory experiment, the growth efficiency wa s significantly higher in the R. philippinarum-group than in the M. gallopr ovinciallis- and the C. gigas-groups. Thus, H. okudai is suggested to selec t prey to maximize the growth.