The current distribution and abundance of the 40 species of Goodeidae fishes known from Mexico are described, and a total of 84 Evolutionarily Significant Units (ESUs) is designated within these species. Two species and four ESUs are likely extinct with no captive populations, and three species and eight ESUs are probably extinct in the wild but have at least one captive population in Mexico, the United States, or Europe. Of the 35 extant species, the analyses indicate that nine should be considered as critically endangered, 14 as endangered, nine as vulnerable, and only three as least concern. Twenty-seven of these species have experienced substantial declines in distribution or abundance or both since 2000, and only eight appear to have remained relatively stable. Of the 72 extant ESUs, our analyses indicate that 29 should be considered as critically endangered, 21 as endangered, 18 as vulnerable, and only four as least concern. Brief summaries of the historic and current distributions and abundance of each species are provided, as well as ESU. Three strategies are recommended to conserve Mexican goodeids: protect the best-quality remaining habitats where goodeids still persist, restore degraded habitat and re-introduce species or ESUs where practical, and establish captive populations to ensure continued survival of the many species and ESUs that will almost inevitably go extinct in the coming years. Limited resources require cooperation and collaboration between scientists, conservationists, and aquarium hobbyists for successful captive maintenance.

We explore the trophic role that a diverse sympatric group of fishes in the genus Chirostoma play in a large, shallow lake in central Mexico, Lake Chapala. We use δ13C and δ15N stable isotope - based food web analyses to explore how they relate to other components of the Lake Chapala ecosystem. We find five Chirostoma species in top trophic levels of the Chapala food web compared to other fishes, relying on a combination of zooplankton, fish and benthic resources as energy sources. Food web metric analyses showed generally overlapping trophic niches for members of Chirostoma, especially in terms of δ13C. However, C. jordani had lower mean δ15N isotopic values than C. promelas. As a group, "pescados blancos" (C. sphyraena and C. promelas) also had higher δ15N signatures than "charales" (C. consocium, C. jordani and C. labarcae) reflecting greater piscivory, but these differences were not strong for all food web metrics used. Trophic overlap among species of Chirostoma in Lake Chapala raises questions about the forces that might have led to a morphologically diverse but functionally similar and monophyletic group of species.

Central Mexico, home to a unique and imperilled freshwater fish fauna, high in endemism, is also a very densely populated region with considerable human activity. Aquatic systems in the region have been heavily disturbed by human activity in the form of species introductions, pollution, and habitat modification, which has resulted in the extirpation of native fishes and the alteration of the native fish fauna. An analysis of the roles of these factors in the decline of the fish fauna and an overview of its conservation status are presented. Both current and historic fish assemblages were characterized and water physicochemical parameters recorded at 62 localities within the region. Water quality, hydrological modification, and the presence of introduced species were used as variables in a linear model to explore their respective influence on the integrity of local fish assemblages. Analyses suggest that both water quality and the presence of introduced species have had adverse impacts of similar magnitude on the conservation status of native species, whereas hydrological modification has had no statistically significant effect. This survey revealed the profound alteration of the fish fauna. Only 40% of the expected native populations were found, and only 30% of the sampled assemblages were free of introduced species. As little as 17% of the sampled assemblages were taxonomically intact. The mean species richness per locality was only half of that indicated by historical records. The conservation value of springs, where many threatened microendemics can still be found, is highlighted, and we argue that their small size and isolation make them key targets for conservation efforts.