Pumpkinseed sunfish (Lepomis gibbosus) counter spiny cladoceran (Bythotrephes longimanus) defenses

Abstract

How do native species react to the presence of an invader? Consumption by resident fish is important in determining the yearly mortality of the invasive cladoceran Bythotrephes. In aquarium experiments, we discovered that small pumpkinseed sunfish (Lepomis gibbosus) were efficient at removing spines from Bythotrephes longimanus and consuming the adults. Experiments quantified how frequently pumpkinseeds showed successful removal of spines, and compared predatory performance relative to other species of fish. We also checked if Bythotrephes' resting eggs pass through the guts of pumpkinseeds in viable condition. The experiments revealed that pumpkinseed sunfish (45–70 mm total length, TL) from two geographic regions removed spines 87% of the time. Spine-handling techniques allowed pumpkinseeds to consume Bythotrephes faster than other species of small (<70 mm, TL) fish [yellow perch (Perca flavescens) and smallmouth bass (Micropterus dolomieu)]. Forty three percent of Bythotrephes’ resting eggs fed to pumpkinseeds passed through digestive systems intact, a property shared with other fish species. Our findings suggest that a native fish that possesses specialized morphology and behavior for hard-shelled prey manipulation (mollusk consumption) is pre-adapted to counter Bythotrephes’ spine defense. The studies raise two questions: 1) to what degree does pumpkinseed predation influence the geographic distribution of Bythotrephes, and 2) could pumpkinseeds become an effective biological control agent?