Limnetica 32

In the Moctezuma river, Central Mexico we recorded thirty five species of fish, corresponding to a γ diversity of 2.5. The river basin is located in the biological transition zone between both America’s bioregions. The highest α diversity was found in the ecotope Jalpilla (H ′ = 1.58), inside the section of the river Matlapa. Between sub-basins, the greatest β diversity was located in the river Huichihuayán (H ∗ = 2.36). Cichlasoma cyanoguttatum, Cichlasoma pantostictum, Cichlasoma steindachneri, Gambusia marshi, Ictalurus australis, Poecilia formosa and Poecilia reticulata were new records for the basin. Fish distribution was classified in six meta-basins. The most diverse family was Poeciliidae (14 species). Poecilia mexicana was the most abundant species followed by Astyanax mexicanus. Fifty one percent of the species were Neotropical, 20 % Nearctic ones; 25.7 % were native; only 2.8 % were deliberately introduced. Chirostoma jordani and Notropis sallei were recent introductions from the Lerma river. Changes in habitat, channelization for agriculture, water transfers between rivers Lerma and Moctezuma, and the deliberate or accidental introduction and translocation of eight species, were the main reasons of the displacement and reduction in the distribution of the endemic species. Three of the recorded species are protected by Mexican environmental laws: Cichlasoma labridens, C. steindachneri and I. australis. Action plans to preserve fish community and the ecological processes at different territorial and time scales (meta-basin, basin and sub-basin) are proposed.