Temporal and spatial variations and environmental factors influencing the structure of tidepool fish assemblages were quantitatively investigated at Iparana beach, northeast Brazilian coast. The majority of the tidepool fishes sampled were suprabenthic juvenile individuals of great mobility. We recorded during monthly diurnal underwater visual censuses a total of 4,750 fish from 26 species, represented mainly by partial residents from the families Scaridae, Haemulidae, Gerreidae and Pomacentridae. The number of species and individuals showed significant variability among tidepools as a response to variations in their volume and type of substrate cover. The greatest species abundance and richness associated with rocks covered with algae suggested that substrate complexity is one of the main factors defining the spatial structure of the tidepool ichthyofauna. Temporal variability in species abundance and richness was associated with changes in salinity levels due to seasonal rainfalls. A higher number of juvenile fishes from December to May in our samples corroborate the hypothesis that the tidepools act as nursery sites. Therefore, the species associations found in this study and their relation to seasonal and spatial discontinuities may be partly explained according to their habitat requirements and reproductive cycles.