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In a series of experiments, we examined feeding behavior of captive great blue herons Ardea herodius and estimated their ability to affect commercial production of fingerling channel catfish Ictalurus punctatus. Specifically, we determined the following: (1) the biomass of channel catfish fingerlings necessary to maintain the body mass of wild-caught captive great blue herons, (2) capture rates of captive great blue herons foraging on channel catfish fingerlings, (3) evaluation of the losses of catfish fingerlings to heron predation, and (4) the effects of selected catfish pond conditions on heron capture rates and body mass changes. Consistent with previous studies, captive herons required approximately 300 g of live catfish daily to maintain their body mass. Based on evaluation of seine haul indices and inventory data, there was no significant difference (P> 0.05) in numbers of catfish lost over time between control ponds in which herons were excluded and test ponds where herons foraged freely, even though herons foraged on test ponds at a density almost twenty times greater than the average density reported on commercial facilities. Herons captured significantly fewer fish on control ponds than on ponds with ‘‘diseased’’ catfish (catfish temporarily disabled by subcutaneous air injections) or ‘‘undesirable’’ fish (bluegills Lepomis macrochirus; P = 0.0001 and 0.0003, respectively). Herons also lost significantly (P = 0.0369) more body mass on control ponds than on ‘‘undesirable’’ fish ponds. Our findings suggest that unhealthy catfish or undesirable fish are preferred prey for great blue herons. Heron inefficiency in preying on healthy catfish may limit their impact on fingerling catfish production, but additional studies are needed to substantiate these findings under actual field conditions.