T.W. Spier and R.C. Heidinger, Fisheries Research Laboratory and Department of Zoology, Southern Illinois University, Carbondale, IL 62901

Abstract. The black crappie Pomoxis nigromaculatus and white crappie P. annularis are popular sportfish in the U.S., but managing their communities can be difficult. Determining the composition of the communities may be troublesome since they may include a significant number of hybrids. Also, crappie tend to overpopulate and produce stunted populations consisting of multiple age classes. Few studies have reported the extent of crappie hybridization in Midwestern U.S. reservoirs. Black and white crappie are sympatric in many Illinois impoundments and thus have the opportunity to hybridize. Allozyme electrophoresis was used to examine the extent of crappie hybridization in Illinois. Seven hundred crappie from 7 impoundments were screened at 3 diagnostic loci. Between 0 and 5% of crappie were found to be hybrids. Stunted black and white crappie from 2 Illinois populations were PIT tagged, stocked into experimental ponds, and offered high densities of fathead minnows (Pimephales promelas). Linear regression analysis showed that older crappie did not grow as well as younger crappie of similar size (black crappie p = 0.0001, R² = .4713). These results suggest that crappie communities in Illinois do not contain a substantial amount of hybrids. Also, the growth of crappie in communities which consist of older cohorts may not respond to management strategies as quickly as those which contain younger age classes.