The structure of the fish community of Raya Lagoon was analysed during 1990. Monthly catches were made in the mouth and inner part of the lagoon, using a 6 mm-mesh beach seine net, 31 m in length and 2.15 m in height. A total of 19,516 specimens, corresponding to 30 families, 50 genera and 62 species, were caught. The most numerous were Anchoa hepsetus, 36.60%, and Eucinostomus gula, 23.51%. ... [Show full abstract] Numerical diversity fluctuated between 1.74 and 3.51 bits/ind diversity in terms of weight, between 1.91 and 3.5 bits/ind, species richness, between 3.45 and 4.29; equitability, between 0.48 and 0.74; redundancy, between 0.28 and 0.67; dominance, between 42.25 and 80.61%. The dominant species were Eucinostomus gula, Diapterus rhombeus, Anchoa hepsetus, Archosargus rhomboidalis, Arius herzbergii and Xenomelaniris brasiliensis. Of the species found, 41.94% were occasional visitors, 30.65% were cyclical visitors and 27.42% were permanent residents. Likewise, 40.32% were first order consumer species; 40.32%, second order consumers; 19.36%, third order consumers. The low percentage of permanent residents indicates this area’s instability.