The Chiapas - Fonseca freshwater ecoregion, FEOW ecoregion 201, is a tropical and subtropical coastal-river ecoregion on the Pacific slope of southern Mexico and northern Central America. It extends from the Río Pijijiapan basin on the Pacific coast of Chiapas southeastward along the Pacific slope of Guatemala, El Salvador, and Honduras to the Gulf of Fonseca. In Mexico, it includes the Pacific coastal drainages of Chiapas, where short rivers descend from the Sierra Madre de Chiapas toward coastal plains, lagoons, mangroves, and estuaries.

The ecoregion’s habitats include mountain streams, canyon creeks, rocky runs, pools, short lowland rivers, coastal lagoons, crater lakes, mangroves, tidal flats, estuaries, and inland salt marshes in hypersaline sediments. Rivers are strongly seasonal. During the rainy season, floods connect channels, wetlands, lagoons, and estuarine habitats; during the dry season, fishes may be concentrated in pools, perennial channels, lagoons, and lowland refuges. Because many basins are short and steep, headwater disturbance can rapidly affect lower river and coastal habitats.

The fish fauna is typical of short Middle American Pacific-slope drainages. It includes poeciliids, cichlids, catfishes, gobies, sleepers, mullets, eels, snooks, and other estuarine-associated or peripheral fishes. In surveys of Pacific-slope rivers of Chiapas, Poeciliidae were the dominant family, reflecting the importance of livebearers in warm lowland channels, seasonal streams, pools, lagoons, and disturbed habitats. Species of Poecilia, Poeciliopsis, Priapella, Heterandria, and related genera may occur in different parts of the broader regional context, depending on drainage and locality.

Peripheral and estuarine-associated fishes are also important. Gobies, sleepers, mullets, eels, snooks, and other coastal fishes may use the lower parts of rivers, lagoons, mangroves, and brackish reaches. In this ecoregion, estuaries and coastal lagoons are not marginal habitats; they are integral parts of the freshwater-to-marine gradient that supports much of the regional fish diversity.

Cichlids are native and important in the Chiapas-Fonseca ecoregion, but they do not form a lake-type species flock. In the Mexican portion, the most important native cichlid is Amphilophus trimaculatus, the three-spot cichlid. This species occurs in Pacific-slope drainages of Middle America from Mexico to El Salvador and is associated with lowland rivers, lagoons, marshes, and brackish-influenced habitats.

Southeastward, in Guatemala, El Salvador, and Honduras, the broader ecoregion includes additional Middle American cichlids, depending on drainage and locality. These may include species of Amatitlania, Astatheros, Cribroheros, Cryptoheros, Parachromis, Vieja, and related genera. However, these records should not automatically be applied to the Mexican portion of the ecoregion. Chiapas itself encompasses multiple freshwater ecoregions, so locality and drainage data are essential when assigning species to Chiapas-Fonseca.

Introduced fishes should be treated separately from the native fauna. Tilapiines such as Oreochromis niloticus and Oreochromis mossambicus may occur in reservoirs, ponds, canals, irrigation systems, or modified lowland waters. Other introduced fishes may arrive through aquaculture, stocking, aquarium releases, or accidental movement between basins. These species can affect native fishes through competition, predation, disease, habitat disturbance, and changes in food webs.

Conservation priorities include protecting mountain streams, canyon creeks, perennial pools, coastal lagoons, mangroves, estuaries, riparian vegetation, and natural seasonal flow. Major threats include deforestation, agriculture, cattle ranching, water abstraction, dams, reservoirs, mining, sedimentation, sewage, urban pollution, agrochemical runoff, wetland loss, invasive fishes, and altered dry-season flow. For FFM, Chiapas - Fonseca should be treated as the Pacific-slope Chiapas ecoregion: a short-river, lagoon, estuary, livebearer-rich, cichlid-bearing system in which Amphilophus trimaculatus is the principal native cichlid in the Mexican sector.

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.