Density Dependence Affects Growth Of Stocked Channel Catfish As Revealed By Stable Isotope Analysis

Food web structure of two medium size Oklahoma reservoirs was assessed to examine trophic ecology of channel catfish Ictalurus punctatus in relation to stocking and potential competitors; bluegill Lepomis macrochirus, flathead catfish Pylodictis olivaris, and crappie Pomoxis spp.  Components of the reservoir food webs, including aquatic vegetation, zooplankton, benthic invertebrates, Asian clam Corbicula fluminea, and fish were sampled from each of the reservoirs in 2011 and analyzed for δ13C and δ15N as trophic level indicators.  Results from a Bayesian mixing model indicated channel catfish and bluegill were predominately invertivores; whereas, flathead catfish and crappie were a trophic level higher, consuming aquatic invertebrates and fish.  Stocked channel catfish trophic level was a function of density of similar-sized wild fish, indicating intraspecific competition.  Although channel catfish were predominately invertivorous, some larger channel catfish contained fish in their diets.  Linear regression models were developed to relate trophic level with total length.  Based on these results, stocked channel catfish appeared to acclimate to a wild diet relatively rapidly when instraspecific competition was low, leading to increased growth rates.