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The structure of fish communities inhabiting separate meadows of the seagrasses Zostera capricorni Aschers. and Posidonia australis Hook f. in Botany Bay, central New South Wales, was studied over a 2-year period using a number of community parameters. The heterogeneity, species richness and total abundance of fishes were not found to be significantly different between the two seagrass habitats, although more species and more individuals were associated with Zostera. The number of species, abundance of individuals and total biomass were all significantly greater in both habitats during summer, and total biomass was significantly greater in the Posidonia. Ordination of species abundance data separated samples from the two habitats. In general, larger species of the Gobiidae and Syngnathidae were diagnostic of Posidonia and smaller members of these families were unique to, or more abundant in, Zostera. Occurrence, abundance and biomass data were used to identify the 20 dominant members of the fish community in each habitat. About 50% of the dominant fish species associated with each seagrass habitat were of some economic importance. Such species were usually residents or transients and made up most of the biomass in each habitat. Adults of these dominant economically important species were most abundant in both seagrass habitats during summer. Juveniles of several economically important species were present in both Posidonia and Zostera meadows. However, marked differences in time of occurrence, size and feeding behaviour of these juveniles between the two habitats suggest that such species use Zostera and Posidonia meadows sequentially. Differences in the structure of the communities, and utilization of resources by juveniles of several economically important species, appear to be related to variations in the structural complexity of the canopies created by the two seagrasses.