ONTOGENIC CHANGES IN PREY SELECTION AND VISUAL-ACUITY OF THE YELLOW PERCH, PERCA-FLAVESCENS

Age-0 yellow perch, Perca flavescens, shift from pelagic to demersal waters of Oneida Lake, New York, between late June to mid-July, when they reach standard lengths of 24-31 mm. The timing of this habitat shift coincides with the size range over which yellow perch achieve a degree of visual resolution that nearly equals that of adult yellow perch, from 174 min of arc in newly hatched larvae to 9-12 min in adults. This visual improvement is reflected in the yellow perch's diet, which consists of an increasingly wider range of prey sizes and types. If twin cones are counted as functionally separate photoreceptors, there is a significant improvement of the calculated visual acuity in larval fish with lenses <1 mm in diameter but not in older fish with larger lenses. During its rapid growth phase the most optimistic calculation of visual acuity in a young yellow perch is insufficient to explain the feeding success necessary at this time. We suggest therefore that young yellow perch spend more time in search of prey than their adult counterparts.