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Open Access Research

Parasite-induced aggression and impaired contest ability in a fish host

V N Mikheev1*, A F Pasternak2, J Taskinen3 and E T Valtonen3

Author Affiliations

1 Laboratory of Behaviour of Lower Vertebrates, Institute of Ecology and Evolution, Russian Academy of Sciences, 33 Leninskii pr, 119071 Moscow, Russia

2 Laboratory of Plankton Ecology, Institute of Oceanology Russian Academy of Sciences, 36 Nakhimovskii pr, 117997 Moscow, Russia

3 Department of Biological and Environmental Science, University of Jyväskylä, PL 35, 40351 Jyväskylä, Finland

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Parasites & Vectors 2010, 3:17  doi:10.1186/1756-3305-3-17

Published: 15 March 2010

Abstract

Background

Success of trophically transmitted parasites depends to a great extent on their ability to manipulate their intermediate hosts in a way that makes them easier prey for target hosts. Parasite-induced behavioural changes are the most spectacular and diverse examples of manipulation. Most of the studies have been focused on individual behaviour of hosts including fish. We suggest that agonistic interactions and territoriality in fish hosts may affect their vulnerability to predators and thus the transmission efficiency of trophically transmitted parasites. The parasite Diplostomum spathaceum (Trematoda) and juvenile rainbow trout, Oncorhynchus mykiss, were used to study whether infection can alter aggression rates and territorial behaviour of intermediate fish hosts.

Results

The changes in behaviour of rainbow trout, Oncorhynchus mykiss, infected with an eye fluke Diplostomum spathaceum (Trematoda), was monitored over the course of an experimental infection for 1.5 months. At the beginning of their development, not yet infective D. spathaceum metacercariae decreased the aggressiveness of rainbow trout. By the time that metacercariae were fully infective to their definitive hosts, the aggressiveness increased and exceeded that of control fish. Despite the increased aggressiveness, the experimentally infected fish lost contests for a territory (dark parts of the bottom) against the control fish.

Conclusions

The results obtained indicate that the parasitized fish pay the cost of aggressiveness without the benefit of acquiring a territory that would provide them with better protection against predators. This behaviour should increase transmission of the parasite as expected by the parasite manipulation hypothesis.