Ecosystem effects of three omnivorous fishes, gizzard shad Dorosoma cepedianum, smallmouth buffalo Ictiobus bubalus, and river carpsucker Carpiodes carpio were examined in Lake Texoma (Oklahoma-Texas). Because a large proportion of the total fish biomass in this reservoir (> 50%) is comprised of these fishes, they may potentially play an important role in the functioning of this ecosystem. The objectives of my study were to examine interspecific differences in excretion rates of limiting nutrients (nitrogen and phosphorous) among these fishes. Mean excretion rates by gizzard shad were greatest for both ammonia-N (9.4 ?mol g^-1h^-1) and phosphate-P (0.11 ?mol g^-1h^-1) and least for smallmouth buffalo (ammonia-N 3.1 ?mol g^-1h^-1 and phosphate-P 0.03 ?mol g^-1h^-1). Ratios of N:P were relatively large in comparison to published values for other taxa. Gizzard shad had the lowest mean N:P ratio (90) and river carpsucker the highest (130). Gizzard shad appear to have the greatest potential to make available limiting nutrients, particularly phosphorous. However, the combined excretion of all species is likely to effect primary productivity when external loading from the watershed is low.