INFLUENCE OF PARASITISM ON THE SHOALING BEHAVIOR OF BANDED KILLIFISH, FUNDULUS-DIAPHANUS

The banded killifish (Fundulus diaphanus), with other freshwater fish species, is the second intermediate host of the digenean trematode parasite Crassiphiala bulboglossa. We investigated whether and how the shoaling behaviour of parasitized killifish is altered in ways that may facilitate transmission of the parasite to its final host, the belted kingfisher (Megaceryle alcyon). In mixed groups of parasitized and unparasitized killifish, parasitized individuals spent less time in shoals, had fewer neighbours within two body lengths, and occurred more frequently in peripheral shoal positions, where they are risk-prone, than unparasitized conspecifics did. After a simulated predator attack with a model of a stuffed belted kingfisher, parasitized individuals did not increase their shoaling tendency and thus had fewer near neighbours than unparasitized fish. These apparent parasite-mediated behavioural modifications in killifish may result in an increased probability of transmission of the parasite to its final, avian host.