Abstract  Variability in community (richness, diversity and evenness) and population (size structure) attributes of discards was evaluated in a shrimp fishery in Celestun Lagoon, Mexico, in different climatic seasons and hydrological zones. Sampling was conducted using two bottom nets with different mesh size codends: 1.3 cm (used in the fishery) and 2.5 cm. Although the shrimp:discard ratio was 1:1 in both cases, total biomass and abundance with the 1.3-cm mesh size were, respectively, 4.6 and 1.8 times higher than with the 2.5-cm mesh size. This result was consistent in time and space. Discards were dominated by fishes [60% in 1.3-cm mesh size and 96% in 2.5-cm mesh size, mainly Cichlasoma urophthalmus (Günther), Eucinostomus gula (Quoy & Gaimard) and Lucania parva (Baird & Girard)] and shellfishes (40% in 1.3-cm mesh size and 4% in 2.5-cm mesh size, mainly Palaemonetes spp. and Callinectes spp.). The highest discards were registered the nortes season with both mesh sizes. The 1.3-cm mesh size retained significantly smaller sizes than the 2.5-cm mesh size in six of the eight most important species. An increase in mesh size, together with a fishery closure during the nortes season, are suggested to mitigate the impact of the fishery on the discarded fauna.