Feeding behavior of hatchery-reared and wild Japanese flounder juveniles was compared to determine whether behavioral differences might lead to higher vulnerability of reared flounder to predation. Laboratory experiments using a video observatory system were conducted to analyze feeding behavior including quantification of time of swimming in the water column, distance from the initial to settled position, swim-up height from the bottom and the pattern of swimming course. Swimming courses were classified into 3 types according to the extent that flounder returned to their initial position. Wild flounder showed rapid feeding behavior and returned near the initial position, while reared flounder spent significantly longer periods in the water column and settled on the bottom at a distance from the initial position. These findings suggest that hatchery-reared flounder are more vulnerable to predators than wild flounder due to longer exposure in the water column and frequent change of settling location. Differences in feeding behavior found between reared and wild flounder may explain high mortality of hatchery-reared flounder immediately after release.
