SYNOPSIS. We evaluated the effects of maternal environment on offspring size and composition in three species of poeciliid fishes. We chose food availability as the environmental factor for study. Mature females were assigned to either high or low food for an interval of time, then randomly reassigned to high or low food, with the restriction that there be equal numbers in each of four treatments: high-high, high-low, lowhigh, and low-low food availability. The three species chosen for study differ in the pattern of maternal provisioning. Poecilia reticulata and Priapichthys festae mothers provide all resources necessary for development as yolk, prior to fertilization. In contrast, Heterandria formosa mothers continue to provision the young throughout development. These species also differ in whether or not they have superfetation, or the ability to carry multiple broods of young in different stages of development. P. reticulata does not have superfetation while the other two species do. We were interested in whether the pattern of maternal provisioning or superfetation influenced the maternal effect. The two lecithotrophic species responded to low food by producing larger young with greater fat reserves. H. formosa, the matrotrophic species, responded to low food by producing smaller young. We propose that the production of large young in the face of low food availability might represent adaptive plasticity; matrotrophy might represent a constraint that prevents such an adaptive response. Superfetation had no impact on this maternal effect.