Abstract

The composition of the assemblies of fish during two annual cycles (2004 - 2005 and 2007 - 2008) in a network of 10 stations inside the system lagoon in the Reserve of the Biosphere Ría Lagartos, Mexico was studied. In every site the hydrological parameters were registered (temperature, salinity and dissolved oxygen) and the fish were collected with a beach seine (15 m; 2.5 cm mesh size). Seasonal significant differences were registered in the temperature and the dissolved oxygen, whereas spatially the salinity was the significant variable that showed marine values in the zone of the mouth to more than 100 in the interior of the lagoon. A total of 11,187 individuals were collected with a weight of 138 kg, of which a total of 32 families and 63 species were identified. The numerical abundant species were Floridichthys polyommus and Cyprinodon artifrons (55 %), whereas Sphoeroides testudineus was the one with the highest contribution to the biomass (71.5 %). The composition of species was integrated in great majority by estuarine and eurihaline marine species. Eight species turned out to be dominant by means of the IVI and as a whole they contributed more than 75%. The structure of the assemblages was principally spatial, for that reason the salinity was the variable that was best related to the abundance of the species (0.861, CCA). The hipersaline habitat was the one that contributed to the highest density, whereas the channel and marine were those that contributed more to the biomass. It is concluded that the high species richness registered in the lagoon system, is due to habitat heterogeneity and to the protection that the system offer to the fish in larval and juvenile stages.

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