Mortality of larval bluegills Lepomis macrochirus from predation was measured in 56 nests guarded by males and 21 nests from which the male guard was removed. Mortality was significantly greater in unguarded nests (median = 68%) than in guarded nests (median = 14%). Fish traps placed in unguarded nests captured significantly more predators than traps placed in guarded nests. Bluegills (3–12 cm total length) were the most abundant nest predators. Pumpkinseeds Lepomis gibbosus (7–11 cm), largemouth bass Micropterus salmoides (4–5 cm), and whitefin shiners Notropis niveus (5–6 cm) also were nest predators. Nest preparation by male bluegills exposed coarse gravel (8–32 mm diameter) and pebbles (32–64 mm) in nest substrate and removed particles smaller than 2 mm. Particles larger than 8 mm provided suitable interstitial space to accommodate bluegill larvae. Survival of larvae was directly correlated with the proportion of coarse substrate in the nest.