The Astyanax species complex has two morphs: a blind, depigmented morph which inhabits caves in México and an eyed, pigmented surface-dwelling morph. The eyed morph can also be found in a few caves, sometimes hybridizing with the cave morph. This species complex has arguably become the most prominent model system among cave organisms for the study of evolutionary development and genomics. Before this study, 32 caves were known to be inhabited by the cave morph, 30 of them within the El Abra region. The purpose of this study was to conduct new surveys of the area and to assess some unconfirmed reports of caves presumably inhabited by troglomorphic fish. We describe two new localities, Sótano del Toro #2 and Sótano de La Calera. These two caves comprise a single hydrologic system together with the previously described cave of Sótano del Toro. The system is inhabited by a mixed population of troglomorphic, epigeomorphic, and presumably hybrid fish. Furthermore, Astyanax cavefish and the mysid shrimp Spelaeomysis quinterensis show a phylogeographic convergence that supports the notion that the central Sierra de El Abra is a biogeographical region that has influenced the evolutionary history of its aquatic community across species. The presumptive location of the boundaries of this biogeographical region are identified.

México es reconocido como un país mega-diverso donde los peces constituyen el grupo de vertebrados conmayor riqueza de especies, ya que en la actualidad se conocen un total de 2 763 especies en el país, y éstas representanaproximadamente el 9.8% del total de los peces conocidos en el mundo. Cada pez tiene una historia evolutivaúnica, por lo cual existe una gran diversidad de formas que ocupan gran parte de los también diversos ecosistemasacuáticos del territorio nacional. En este trabajo se ofrece el panorama actual de la ictiofauna mexicana, que incluye505 peces dulceacuícolas, 2 224 marinos y 563 estuarinos y vicarios; caracterizados como especies de distribuciónde las regiones neártica, neotropical o de transición en la parte continental y por 7 provincias marinas. También semuestra la diversidad de las formas, reproducción y comportamiento de algunos grupos de especies, complementadacon cuadros acerca de la clasificación taxonómica y ecológica de la diversidad íctica, así como una gráfica sobre elincremento del conocimiento de los peces en el país desde el siglo XVIII.

This paper presents a list of the exotic fish species introduced in Mexican aquatic systems. This list is the result of the systematized information contained in several databases of ichthyological collections around the world and different publications. A total of 104 species were found, distributed in 19 families and 51 genera. The most species-rich were Cyprinidae with 22 species, Poeciliidae (19 species), Cichlidae (15 species) and Centrarchidae (13 species). A map and an electronic database were created based on the knowledge of the species, showing the known introductions of exotic fishes in the country. The information was obtained from a database stored in the Colección Nacional de Peces IBUNAM, which can be accessed online. This study has a high importance for the knowledge of the exotic fish fauna of Mexico and its current status.

Consumer‐driven nutrient recycling can have substantial effects on primary production and patterns of nutrient limitation in aquatic ecosystems by altering the rates as well as the relative supplies of the key nutrients nitrogen (N) and phosphorus (P). While variation in nutrient recycling stoichiometry has been well‐studied among species, the mechanisms that explain intraspecific variation in recycling N:P are not well‐understood. We examined the relative importance of potential drivers of variation in nutrient recycling by the fish Gambusia marshi among aquatic habitats in the Cuatro Ciénegas basin of Coahuila, Mexico. There, G. marshi inhabits warm thermal springs with high predation pressure as well as cooler, surface runoff‐fed systems with low predation pressure. We hypothesized that variation in food consumption among these habitats would drive intraspecific differences in excretion rates and N:P ratios. Stoichiometric models predicted that temperature alone should not cause substantial variation in excretion N:P, but that further reducing consumption rates should substantially increase excretion N:P. We performed temperature and diet ration manipulation experiments in the laboratory and found strong support for model predictions. We then tested these predictions in the field by measuring nutrient recycling rates and ratios as well as body stoichiometry of fish from nine sites that vary in temperature and predation pressure. Fish from warm, high‐predation sites excreted nutrients at a lower N:P ratio than fish from cool, low‐predation sites, consistent with the hypothesis that reduced consumption under reduced predation pressure had stronger consequences for P retention and excretion among populations than did variation in body stoichiometry. These results highlight the utility of stoichiometric models for predicting variation in consumer‐driven nutrient recycling within a phenotypically variable species.