若狭湾におけるカレイ目魚類の初期生活史の研究 ＶＩ ヒラメの初期生活史

Abstract

The early life history of a flounder Paralichthys olivaceus (TEMMINCK et SCHLEGEL)was studied in the western Wakasa Bay, the Japan Sea. General morphology and characteristics of the larvae and juvenile ranging from 3.25mm to 13.20mm BL, were described. The characteristic features of this fish in early larval stages were elongations of the first 5 dorsal fin rays and distribution patterns of melanophores on the body surface. There is some variation in relationship between stage and boby length in larvae, especially at the late metamorphosis stage. It may mean the variation in the size at settlement. Judging from records of occurrence of early larvae, actual spawning may occur in the western Wakasa Bay during a relative long period from March to May. Early postlarvae were caught mainly off the coast of Wakasa Bay, and late postlarvae were caught mainly in the nearshore regions. In the period of pelagic larval stage, an inshore movement must have taken place. Early juveniles were captured in the shallower water of the estuary of Yura River, and this area may be their nursery ground. Annual occurrence of larval occurrence showed remarkable differences from year to year. Analyses of the gut content showed that the food items were copepod nauplii in early postlarvae, Oikopleura spp. in late postlarvae, and copepods and mysids in early juveniles. Some considerations on the daily food intake of the larvae under natural conditions were discussed.