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The synchronizing between formation of mesoscale hydrographic structures and fish spawning could increase fish larvae survival, as the hydrographic structures could act as a retention or dispersion mechanisms. Same structures enhance the formation and permanence of contiguous larval habitats, suitable for larval development, which are occupied by different larval fish assemblages (LFAs).This work analyze the effect of hydrographic structures on the three-dimensional fish larvae distribution in the Midriff Archipelago region (MAR) of the Gulf of California during the winter mixed anticyclonic phase (February 2007), stratified cyclonic phase during the summer (August 2005), and the low dynamic and productive transition stage between them (June 2006). Permanence from the winter trough the summer of the vertical mixing zone and the frontal system is documented, which presented a seasonal evolution in its position, strength and extension. Frontal system evolution highly influenced the physical-biological dynamics of the zone, and favored formation of associated structures as eddies, filaments and meanders in different seasons where high fish larvae abundance and species richness all-water column spots where found.A total of 20,046 of 169 taxa where identified. LFAs where identified each season using cluster analysis based on the Bray-Curtis similarity index. Its three-dimensional distribution was mapped and overlapped with physical variables distributions to found relations between them. Four LFAs were present each season, and they occupied three different recurrent larval habitats: south zone of the MAR, occupied by wide and southern exclusive distribution species as Scomber japonicus, y Vinciguerria lucetia; oceanic zone, occupied by dominant species, the epipelagic Engraulis mordax during the winter, and wide distribution mesopelagic Leuroglossus stilbius, Triphothurus mexicanus, y Benthosema panamense; and when the frontal system position favored and associated eddie formation, this was an specific larval hbitat, occupied by the richest LFA, including species distributed only into this structure.Results of this work showed the importance of the frontal system role in physical-biological dynamics on the MAR, and the profound effect of the mesoscale hydrographic structures over the fish larvae abundance, and which sometimes represents itself specific larval habitats, transport mechanisms, or limits on the distribution of LFAs.

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