Alimentary tracts were examined of 1010 carp collected with gill and trammel nets by commercial fishermen from four riverine reservoirs, and 211 adult and 45 young carp from Lake Carl Blackwell, a headwaters reservoir. The alimentary tract contents of carp in five Oklahoma reservoirs contained algae, plant fragments, seeds, entomostraca, chironomids, Chaoborus, pelecypoqs, caddisflies, Ceratopogonidae, animal fragments, and organic and inorganic matter. Terrestrial insects were of rare occurrence. The major volumetric constituents in the alimentary tracts of carp from the riverine reservoirs Grand, Fort Gibson, Eufaula, and Texoma Reservoirs were: unidentified organic matter (65.5%), animal fragments (12.5%), plant fragments (10.1%), entomostraca (3.8%), algae (1.9%), pupae (1.1%). Adult carp collected by electrofishing from Lake Carl Blackwell, a headwaters impoundment, contained on a volumetric basis, 41.7% organic detritus, 35.9% plant matter (18.8% plant fragments, 11.8% seeds, 5.3% algae), 5.0% entomostraca, 3.1% chironomids, 0.2% Chaoborus, 8.9% animal fragments. Organic detritus was also the major volumetric constituent (49.8%) of the 45 young carp «9 inches total length) examined from Lake Carl Blackwell. Stomachs of young carp contained no algae, and fewer seeds and plant fragments than the adults, and a considerably larger volume of entomostraca (19.2% of the total volume). Carp seem to feed on the unconsolidated portion Df the substrate. Organisms like tubificids, and burrowing mayflies and odonates, requiring consolidated substrate, were not present. The Cladoceran genus Chydorus which lives in the flocculent material at the substrate-water interface, predominated over limnetic genera like Bosmina and Daphnia. Seeds were very abundant in Carl Blackwell carp following a spring flooding of marginal vegetation. No fish eggs, fish fry, dragonflies, mayflies or oligochaetes were found in carp tracts, and only two tracts contained fish. There was considerable monthly and inter-reservoir variation in abundance of most items. In Lake Texoma, peak abundance of Cladocera and Copepoda in. carp tracts coincided with the maximum inflow of water. In the Oklahoma reservoirs studied, carp probably have little effect on water quality or availability of aquatic plants. Food competition by carp is probably greatest with young game fishes, young and adult river carpsucker and smallmouth buffalo. The high relative abundance of carp, carpsucker and smallmouth buffalo is attributable to their consumption of particulate organic matter, and the community of decomposer organisms and the invertebrates which feed on the organic detritus. Direct competition with game fish would occur among larval game fish when food scarcity during the critical period could limit year class strength. Indirect food competition occurs between carp and larger invertebrate life which are utilized by juvenile game fishes.
