BASIC STUDIES ON RELEASE TECHNIQUES OF HATCHERY-REARED JAPANESE FLOUNDER - V - EFFECTS OF STARVATION ON FEEDING-BEHAVIOR AND PREDATION VULNERABILITY OF WILD JAPANESE FLOUNDER JUVENILE

Feeding behavior of wild Japanese flounder juvenile with progress in s tarvation uas examined to determine whether starvation could increase vulnerability of wild Bounder to predation. Laboratory experiments wer e conducted using a video observation system to analyze feeding behavi or of juvenile flounder such as time of swimming to water column, swim ming course and number of attacks in a feeding behavior under starvati on up to 7 days. Experiments showed that longer starved juveniles spen t a longer time in the water column and returned farther from the init ial position. The number of attacks in a feeding behavior increased in a few days after onset of starvation. Fed juvenile Bounders mere not preyed upon by 1- or a-year-old Bounders, while 3 to 7 days starved ju veniles mere preyed upon in the laboratory experiment. These findings suggest that wild juvenile flounder change feeding behavior toward mor e vulnerability to predators with progress in starvation primarily due to longer exposure in the water column and frequent changes of landin g position. These changes in feeding behavior found in the laboratory suggest that high mortality of juveniles would occur associated with s easonal reduction in prey mysid abundance in their nursery ground.