Abstract A 3-year study was conducted of growth and condition of northern largemouth bass Micropterus salmoides salmoides and F1 hybrid largemouth bass (male northern smallmouth bass M. dolomieui dolomieui x female largemouth bass) stocked together in diverse pond treatments. Six drainable 0.4-hectare ponds in southern Illinois were initially stocked with similar numbers of half-sibling largemouth bass and F1 hybrid larvae produced in the laboratory. Most populations were censused and restocked each spring and fall through three growing seasons (1979–1981). Supplementary data were generated by introducing age-1 largemouth bass and F1 hybrids into two larger ponds containing mature populations dominated by largemouth bass and bluegills. Growth of pure largemouth bass was significantly faster than that of half-sibling F1 hybrids in all populations studied each year, regardless of treatment, although third-year growths in the 0.4-hectare ponds were complicated by a differential response to tagging. After the...