Planktivory by bluegill (Lepomis macrochirus) on Leptodora kindti in a small North American lake

Leptodora kindti (Crustacea: Cladocera) is a large species of zooplankton ( 2-18 mm length) that is exceptionally transparent. This transparency is bel ieved to be a means by which it successfully coexists in lakes with plankti vorous fishes. We investigated the gut remains of bluegill ( Lepomis macroc hirus) that had been feeding on L. kindti and Daphnia (D. galeata and D. re trocurva) in the wild (Lake Zurich, Illinois) and found that bluegill readi ly preyed on L. kindti as small as 3-5 mm length, and strongly selected L. kindti over Daphnia galeata and Daphnia retrocurva. The large compound eye of L. kindti is one half to one complete order of magnitude larger than Dap hnia's eye, consistent with the hypothesis that eye area is an important vi sual cue for fishes. Moreover, the slope of the relationship between eye ar ea and body length is an order of magnitude shallower in L. kindti than Dap hnia, suggesting that eye area has been under stronger negative selection i n L. kindti. Results suggest that L. kindti's large and dark eye compromise s the transparent nature of its body.