Marine spatial planning and management processes are important tools for environmental and resource management, providing effective frameworks for considering environmental, social, cultural, institutional and economic variables within a common biogeographic context. The Akanda National Park (ANP) in Gabon, almost exclusively constituted by mangroves, is part of a green belt of protected areas around the capital city of Libreville. The creation of the ANP is considered as an essential tool for the ecosystemic management of fisheries in Mondah Bay, playing nursery function for several exploited fish species. However, this role has never been documented in the mangroves of Gabon. The aim of this study is to describe the spatial and seasonal variability of fish assemblages, to assess ANP mangrove role as a nursery for fish juveniles. Fish sampling was carried out at four different sites in the four hydroclimatic seasons in Gabon using trammel gillnets with different mesh size (10, 27 and 40 mm). Fifty-nine fish species mainly estuarine and marine, first and second level predators were collected whatever the season and the site. The numerically dominant species were Pseudotolithus elongatus, Pellonula leonensis and Parachelon grandisquamis (48% of the total number of individuals), whereas P. elongatus, Chrysichthys nigrodigitatus and Plectorhinchus macrolepis represented the main biomasses (55%). The predominance in the catches of immature individuals of many species of commercial interest and in particular, P. elongatus, P. grandisquamis, C. nigrodigitatus, Eucinostomus melanopterus, Neochelon falcipinnis and Polydactylus quadrifilis, which dominate the community, highlights the importance of Akanda mangrove as a nursery for the juveniles of these species. The results of our study are a first step in understanding the fish communities of a Gabon marine protected area, which can support the decision making management plans, zonation and initiate a monitoring program for the estuarine and marine protected ecosystems.