The plaice Pamlichthys olivaceus is important fishery species in Japan. As the fishing amout of them is declining in a few decades propagation ofthem is doing by means of creation of nursery grounds in the coastal sea. Knowleges of biological character of objective fish is essential for the propagation. The author has continued the basic research to define ecology and physiology of the plaice larvae and juveniles to contribute to effective creation of nursery grounds of them. First of all, the suitable environmental condition and specific gravity (∂t) of eggs and larvae, and swimming speed of larvae of them were examined. Hatch ratio of eggs was the highest on 15℃ in water temperature and on about 42‰ in salinity. Specific gravity of eggs varied between 21 and 27 according to development and of larvae did between 23 and 58 according to growth. Short period swimming speed of larvae increased to about 6cm/s from 1cm/s according to growth. Sustainable swimming speed decreased almost according to time lapse from beginning of measurement. Reaction of larvae to the change of illuminance and to the diffrence of salinity in the tank were examined next by expermental ways. Larvae moved vertically in the transparent plastic pipe according to the change of illuminance and tended to distribute more frequently in the low salinity layer of the density stratiffication tank. Finally, the prey demand of juveniles was examined by both eclogical way and experimental one. Juveniles below 8cm in total length tended to eat only mysids and ones over 10cm do to eat shrimps and fish. Some ideas for creation of the nursery grounds of the plaice were suggested being based on the result of this reserch in addition.
