An important element of the ichthyofauna of warmwater streams of the southeastern United States, the redbreast sunfish is the dominant species of the lower Suwannee and lower Santa Fe Rivers in Florida. Insects formed the bulk of the diet of both populations though opportunistic feeding is suggested by the wide variety of organisms tak.en. Spawning occurs from April through October, with a peak in late spring and summer. Fecundity ranged from 942 to 9968 ova per fish. Mean condition factor (K) was higher for Santa Fe redbreasts than for Suwannee specimens. Lengthwweight relationships for Santa Fe fish were log W =-4.20+2.89 (logL) and logW =-4.06+2.81 (IogL).