Abstract #03
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11/19/04
FW 315
Seppälä, O., A. Karvonen, E. T. Valtonen. 2004. Parasite-induced change in host behaviour and susceptibility to predation in an eye fluke-fish interaction. An. Behaviour. 68:257-263.
The objective of this study was to determine if an infestation of Diplostomum spathaceum (Trematoda) in Oncorhynchus mykiss (rainbow trout) effected the fish’s preferred location in the water column and predatory escape behavior. Test groups were infected with the parasite, while control groups were kept free of any significant parasitic infection. Two experiments were conducted, one judging water-column preference in response to a potential threat (behavior experiment), the other testing the ability of infected vs. non-infected fish to avoid “predation” in the form of people using dip-nets to catch the fish (predation experiment). In the behavior experiment, infected fish did not seem to prefer the surface layers of water, but their escape response and movement toward deeper water after a disturbance was diminished in comparison to the control groups. The predation experiment determined that infected fish were more likely to be caught than uninfected fish. After the conclusion of each experiment, the fish were killed using an overdose of 0.01% MS 222, and the intensity of cataracts (caused by the parasite), as well as the number of D. spathaceum, were calculated. Body length and mass were also determined, and there was no significant difference between the infected fish and the control groups. The most likely mechanism by which D. spathaceum alters the behavior of O. mykiss is by reducing vision through cataract formation. By decreasing sight and increasing susceptibility to predation by piscivorous birds, D. spathaceum facilitates its transfer to the next host in its life cycle.
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