Environmental factors associated with fish assemblage patterns in a high gradient river of the Gulf of Mexico slope

Using multivariate analyses of fish community and environmental data, we explored associations among 13 fish species and 9 ecological guilds and identified ecological gradients that explain patterns in the fish community of the La Antigua River (Veracruz, Mexico). Altitude, distance to ocean, stream width, and water temperature were the most important variables explaining community composition. Sites with high altitudes (> 1 393 m), cold water ( 100 km) and less than 5 m wide were dominated by non-native Onchorhynchus mykiss. Many sites exclusively inhabited by native poeciliids were also narrow ( 80 km, 20oC). Because 7 guilds were exclusive to a single species, results from the guild analysis were very similar to species-specific analyses. Higher species and guild diversity were found in wider sites (> 5 m), sites with lower altitudes (< 600 m), and sites closer to the ocean (< 71 km). Variables related to human influence did not explain trends found in the fish communities.