We excluded predatory fish from a marsh weedbed to evaluate experimentally their impact on invertebrate prey. Gut analyses of wetland fish, including pumpkinseed sunfish (Lepomis gibbosus), brown bullhead (Ictalurus nebulosus), black crappie (Pomoxis nigromaculatus), and common carp (Cyprinus carpio), revealed that large numbers of midge larvae (Diptera: Chironomidae) were consumed. However, our exclusion of these predatory fish from study habitats did not result in midge population increases. On the contrary, fewer epiphytic midges occurred where predatory fish had been excluded (P 0.0043). Populations of midge competitors (especially Planorbidae and Physidae) and invertebrate midge predators (especially Corixidae and Glossiphoniidae) were suppressed directly by fish, and midges that co-existed with fish apparently benefitted indirectly from those interactions. For epiphytic midge larvae, the negative direct influence of fish predation was strong, but positive indirect effects apparently were even more powerful.
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