Feeding on harpacticoid copepods by marbled sole Pleuronectes yokohamae juveniles in the Coastal Ares of Tsugaru Strait, Hokkaido

Monthly changes in the main food items of and biased feeding on adult males of harpacticoid copepods by marbled sole Pleuronectes yokohamae juveniles were examined in the Coastal Area of Tsugaru Strait, Hokkaido, from April t o September 1996 and in May 1997. At Iwabe Fishing Port in May-July 1996 an d May 1997, marbled sole juveniles (less than or equal to 30 mm in SL) fed on harpacticoid copepods, mainly Harpacticus sp. Off Nanaehama Beach in May 1997, juveniles preyed on harpacticoids, mainly Haledinosoma sp. In August , the main food organisms of juveniles (>30 mm in SL) changed from harpacti coids to small benthic crustaceans and polychaetes. Tn September 1996, juve niles fed chiefly on polychaetes. Adult males of Harpacticus sp. and Halect inosoma sp. were found in significantly larger numbers than adult females a nd copepodites (stage I-V) in fish stomachs. Tn contrast, no significant di fference was found in the sex ratio of Harpacticus sp. on the bottom sedime nt at Iwabe. Because adult female harpacticoids in the stomachs of juvenile s had larger body widths than adult males and copepodites, the biased feedi ng on adult males can not be explained by differences in prey size. The spe cific feeding by marbled sole juveniles might have been caused by a behavio ral difference between harpacticoid males and females in their breeding sea son.