RESEARCH PAPER Patterns in the distribution of fish assemblages in Rı ´o Amacuzac, Mexico: influence of abiotic factors and biotic factors Patricia Trujillo-Jime ´nez • Eugenia Lo ´pez-Lo ´pez • Edmundo Dı ´az-Pardo • Julio A. Camargo Received: 6 August 2009 / Accepted: 30 November 2009 / Published online: 13 December 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Patterns in spatial and seasonal distribu- tion of fish communities were analyzed in the Rı ´o Amacuzac, Mexico, and their relationship to environ- mental variables and habitat characteristics. The PCA biplot of the study sites and environmental factors showed the first two axes accounting for 52.93% of the variance. The diagram showed the study sites ordina- tion in environmental gradients. The first axis explained variables related to habitat characteristics and temperature (36.30%) and second axis arranged the sites in physicochemical and water quality envi- ronmental gradients (conductivity, dissolved oxygen, orthophosphates, ammonium, pH) displaying seasonal variation. Fifteen species were recorded, eight of them are exotic. One new record appeared for the Rı ´o Amacuzac: Pterygoplichthys disjunctivus is exotic. Study sites with highest species richness were: 5, 7 and 9 (twelve species each one); while the study sites with low species richness were 1, 2, 3 and 6 (eight species each one). Six of the species were distributed throughout the whole river. Based on the composition of the fish fauna, the study sites form two groups and the analysis of fish species displays three groups according to the Bray–Curtis index. The diagram of the canonical correspondence analysis relates envi- ronmental parameters to the abundance of fish species and showed that the first two axes exhibit 78.31% of the explained variance. Species richness had a spatial pattern associated to the introduction of exotic species for ornamental uses. According to the results of the importance value index (IVI), the dominant species were the poecilids Poeciliopsis gracilis and Heteran- dria bimaculata, small fishes that were introduced in the river. Rı ´o Amacuzac has a biotic alteration in the structure of fish communities due to the invasion of exotic species, representing risks to the integrity of the native fish fauna. Keywords Fish assemblages Á Distributional patterns Á Native species Á Exotic species Á Rı ´o Amacuzac Á Mexico P. Trujillo-Jime ´nez (&) Centro de Investigaciones Biolo ´gicas, Universidad Auto ´noma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, CP 62209 Cuernavaca, Morelos, Mexico e-mail: trujill@uaem.mx E. Lo ´pez-Lo ´pez Laboratorio de Ictiologı ´a y Limnologı ´a, Escuela Nacional de Ciencias Biolo ´gicas, IPN, Prol. de Carpio y Plan de Ayala, Col. Sto, Toma ´s, DF 11340, Mexico E. Dı ´az-Pardo Facultad de Ciencias Naturales-Biologı ´a, Universidad Auto ´noma de Quere ´taro, Av. de las Ciencias s/n, Juriquilla, Del. Sta. Rosa Jauregui, CP 76230 Santiago de Quere ´taro, Quere ´taro, Mexico J. A. Camargo Departamento de Ecologı ´a, Facultad de Biologı ´a, Universidad de Alcala ´, Ctra. Madrid-Barcelona km. 33,6, 28871 Alcala ´ de Henares, Madrid, Spain 123 Rev Fish Biol Fisheries (2010) 20:457–469 DOI 10.1007/s11160-009-9153-y