EFFECTS OF THE CESTODE SCHISTOCEPHALUS-SOLIDUS ON FOOD-INTAKE AND FORAGING DECISIONS IN THE 3-SPINED STICKLEBACK GASTEROSTEUS-ACULEATUS

Food intake, feeding efficiency, prey profitability and diet choice we re examined in wild-caught three-spined sticklebacks, Gasterosteus acu leatus, infected with the cestode Schistocephalus solidus. Infected fi sh ingested significantly fewer chironomid larvae (bloodworms) before becoming satiated and handled prey for significantly longer than did u ninfected fish. This was especially marked when fish had partially-ful l stomachs. For uninfected fish, large bloodworms were more profitable than smaller ones, regardless of level of satiation. The two prey siz es were equally profitable for infected fish with empty stomachs. Howe ver, for infected fish that had already consumed one prey item, smalle r bloodworms were more profitable; prey profitability was negatively r elated to relative size of the parasite. When offered a choice between large and small bloodworms, uninfected fish consistently chose the la rger. Infected fish with empty stomachs were unselective with respect to prey size, but after eating just one prey item, they showed a signi ficant preference for the smaller prey.