If you visited a lake as a child, you may remember being fascinated by the bluegill and pumpkinseed sunfish swimming under the dock. Sometimes floating almost motionless in the shade, other times darting away from some unseen disturbance, their behavior probably appeared completely random. Careful study, however reveals that each of these closely related species has a distinctive pattern of behavior, particularly during the breeding season. Male pumpkinseeds are solitary animals. Equipped with hard, bony mouthparts well adapted for nipping potential predators. each male is able to protect his own nest site from marauding catfish who might eat he eggs. In contrast, the small, delicate mouthparts of bluegills pose little threat to nest-raiding predators. For protection, bluegills join together in breeding colonies of 50 to 100 males. Strength in numbers may be a good strategy against nest-raiding catfish, but being social poses other problems for male bluegills. Each male vigorously defends a small territory surrounding his nest from the other males, who night slip in and fertilize the female's eggs first.