Damselfishes have served as a model fish for the study of planktivory. The feeding ecology of the diurnal planktivorous Domino Damselfish, Dascyllus albisella (Pomacentridae), was studied in the lagoon of Johnston Atoll (Central Pacific Ocean). Time budgets based on daytime focal observations showed that damselfish spent most (>85%) of their time feeding. Larger D. albisella foraged higher in the water column than smaller damselfish. Individual damselfish fed higher in the water column when the current speeds were lower. All size ranges of damselfish fed primarily on caridean zoea and copepods. The water column was vertically structured with greater caridean and brachyuran zoea concentrations at mid-depths and near the surface than near the bottom. Copepod concentrations, though low, were higher near the bottom than at mid-depths. During the spawning season males had much smaller stomach contents than similarly sized females, which is presumably due to reduced time spent feeding during courtship and nest guarding. These data show an interaction between damselfish size, plankton distributions, feeding heights, and currents. When currents are low, damselfish forage higher in the water column where the flux of plankton is generally greater, with larger damselfish foraging higher than small damselfish. When current speeds increase, damselfish forage closer to the bottom, with less of a difference in the depth distribution of differently sized damselfish. Since damselfish spend most of the daytime hours foraging, the distribution of plankton could be a major selective pressure for larger-sized damselfish.