ヒラメ人工種苗放流技術の開発に関する基礎的研究 Ｖ ヒラメ天然稚魚の摂食行動および被食に及ぼす飢餓の影響

Abstract

Feeding behavior of wild Japanese flounder juvenile with progress in starvation was examined to determine whether starvation could increase vulnerability of wild flounder to predation. Laboratory experiments were conducted using a video observation system to analyze feeding behavior of juvenile flounder such as time of swimming to water column, swimming course and number of attacks in a feeding behavior under starvation up to 7 days. Experiments showed that longer starved juveniles spent a longer time in the water column and returned farther from the initial position. The number of attacks in a feeding behavior increased in a few days after onset of starvation. Fed juvenile flounders were not preyed upon by 1-or 2-year-old flounders, while 3 to 7 days starved juveniles were preyed upon in the laboratory experiment. These findings suggest that wild juvenile flounder change feeding behavior toward more vulnerability to predators with progress in starvation primarily due to longer exposure in the water column and frequent changes of landing position. These changes in feeding behavior found in the laboratory suggest that high mortality of juveniles would occur associated with seasonal reduction in prey mysid abundance in their nursery ground.