In the evolutionary absence of other, competing centrarchid species in California, the Sacramento Perch probably had no need to develop the complex nest-guarding behavior that sunfishes perform. The introduction of eastern sunfish species into California has exposed the Sacramento Perch to the complex world of centrarchid competition. Eastern centrarchids generally build and vigorously guard a nest in a preferred spawning area. The female lays her eggs in the nest and is then chased away by the male, who guards the eggs from predators until they hatch and the fry are free-swimming. Since the Sacramento Perch scatters its eggs on the substrate and may provide little or no protection for the eggs, they are left open to predation by introduced catfish, carp, or other centrarchids.
Eastern species are also more aggressive in their site-selection.
With the increase in the population of eastern species in many habitats in California, the Sacramento Perch is most certainly losing preferred spawning areas to the more aggressive Bluegill and other non-native centrarchids. In aquaria, it has been observed that eastern sunfish will actually chase Sacramento Perch away from preferred spawning areas. Habitat destruction has also contributed to the decline of the Sacramento Perch in its native habitat, The filling of sloughs in the California Delta and the draining of lakes and general reduction of backwater areas have reduced the number of suitable spawning areas substantially. Competition between the fry of the Sacramento Perch and several species of eastern centrarchids for food resources may be another factor in the decline of the species. Studies have indicated that all young centrarchids have similar food preferences, but the eastern centrarchids have evolved more aggressive feeding techniques than the Sacramento Perch, and have been observed chasing the latter from feeding areas.