摘要：Thirteen localities were studied in the Copalita, Zimatán, and Coyula basins, Oaxaca. More than 3 200 decapod crustaceans were captured representing 3 families, 4 genera, and 13 species, including 3 possible new species of Atya and Pseudothelphusa. Abundance, frequency and within basin distribution of species were analyzed. Collecting localities were compared considering their altitude and species composition. The family Palaemonidae had the most species grouped in 1 genus with 8 species, the family Atyidae had 2 genera and 3 species and the family Pseudothelphusidae contributed with 1 genus and 3 species. The most abundant species were Potimirim glabra and Atya sp. 1. Atya margaritacea and Potimirim glabra were the most frequent species occurring in 10 of the 13 sites, Macrobrachium michoacanus occurred in 9, and M. americanum and M. occidentale in 8. The juveniles of Macrobrachium occurred in 9 sites. Species richness and the diversity index tended to increase towards the low portions of the rivers; in the upper reaches these values were low and intermediate to high in the middle portions of the basins. Sampling sites could be classified in 3 groups according to their altitude.
