The Guzmán - Samalayuca freshwater ecoregion, FEOW ecoregion 161, is a xeric freshwater and closed-basin ecoregion in northern Chihuahua, Mexico. It belongs to the Chihuahuan Desert freshwater region and includes endorheic basins, springs, spring runs, temporary waters, desert wetlands, and internally draining valleys rather than a large river flowing to the sea. Important systems include the Laguna de Guzmán complex and neighboring closed basins associated with Casas Grandes, Santa María, Guzmán, Patos, Palomas, and the Samalayuca region.

The ecoregion’s habitats include springs, intermittent streams, playas, temporary pools, marshes, irrigation-influenced waters, and isolated desert aquatic refuges. Surface water may be scarce, seasonal, or highly localized. Some fishes depend on spring-fed habitats, while others use seasonal streams, low-gradient channels, basin-floor wetlands, or temporary waters when available. Because the basins are closed or poorly connected, fish populations can become isolated, and even short distances may separate distinct faunal units.

The fish fauna is highly distinctive and important for desert-fish conservation in Mexico. FEOW notes that Guzmán - Samalayuca is rich in endemic species, as is typical of many endorheic habitats. Strict endemics include Cyprinella bocagrande, Cyprinodon fontinalis, and Gila nigrescens. Near-endemics include Catostomus cahita, Catostomus leopoldi, Cyprinodon albivelis, and Cyprinodon pisteri. These fishes reflect the biogeographic connections among the Chihuahuan Desert, the Sierra Madre Occidental, the Río Yaqui region, and the isolated closed basins of northern Mexico.

Pupfishes are especially important. Cyprinodon fontinalis, the Carbonera pupfish, is one of the signature endemic fishes of the ecoregion and is associated with spring habitats. Cyprinodon pisteri, the Palomas pupfish, is associated with the Lago de Guzmán complex basin in northern Chihuahua. These species illustrate how isolated desert waters can produce localized fishes with very small ranges and high vulnerability to habitat loss, groundwater depletion, and the introduction of nonnative species.

Cyprinids are also central to the fauna. Cyprinella bocagrande, the largemouth shiner, is a strict endemic of the ecoregion, while Gila nigrescens, the Chihuahua chub, is another key endemic. Other regional fishes, including suckers such as Catostomus cahita and Catostomus leopoldi, connect the ecoregion with northwestern Mexican and Sierra Madre-associated drainage histories. The Guzmán Basin has also been associated with forms such as Oncorhynchus mykiss nelsoni, showing that the fauna includes both desert-basin and highland elements.

Cichlids are not native to the Guzmán-Samalayuca ecoregion. The native fish fauna is dominated by desert cyprinids, pupfishes, suckers, trout or trout-like headwater forms in some contexts, and other Nearctic or Chihuahuan Desert fishes. Any cichlid records from the ecoregion should be treated as introduced unless there is clear evidence to the contrary. Tilapiines such as Oreochromis niloticus, Oreochromis aureus, Oreochromis mossambicus, or related aquaculture species may occur in reservoirs, ponds, canals, or modified waters, but they are not part of the native fauna.

Introduced fishes are a serious conservation concern. In closed desert basins, native fishes often persist in small springs, short stream reaches, or isolated wetlands. Introduced predators, competitors, or habitat-modifying species can therefore have strong effects. This is especially important for pupfishes, shiners, chubs, and other species restricted to individual springs, wetland complexes, or short drainage sections.

Conservation priorities include protecting springs, groundwater, temporary pools, marshes, desert wetlands, riparian vegetation, and native fish refuges. Major threats include groundwater extraction, spring drying, agricultural water use, irrigation return flows, livestock impacts, pollution, channel modification, wetland loss, invasive fishes, drought, and climate-driven reduction in water availability. For FFM, Guzmán - Samalayuca should be treated as one of Mexico’s important northern closed-basin desert-fish ecoregions, notable for endemic pupfishes, cyprinids, and localized aquatic refuges rather than for cichlid diversity.

This account is based in part on information from Freshwater Ecoregions of the World (FEOW), © WWF/TNC, used as a reference for educational and scientific purposes. See: http://www.feow.org.