Mexican Highland Lakes - A Global Ecoregion

Unusually high levels of endemism among fish species

About the Area
The Mexican highland lakes ecoregion contains a number of endorheic lakes (those that have no connection to the sea), thermal springs, and streams.

These habitats are characterised by the presence of unusual amphibian and invertebrate species, and fish species radiations in several lakes.

Lake Chapala (Mexico's largest) and the Rio Lerma support fish faunas in which over half of the species are endemic. In addition, the Aguascalientes warm-water aquifer and its associated underground aquatic life underlie portions of the ecoregion.

Local Species
Species include numerous endemic livebearers (family Poecillidae), splitfins (Goodeidae), silversides (Atherinidae), pupfishes (Cyprinodontidae), cichlids (Cichlidae), and characids (Characiformes).

Among the numerous fish species whose distributions are restricted to this ecoregion are Mexican brook lamprey (Lampetra geminis), Lerma chub (Algansea barbata), Leopard splitfin (Xenotaenia resolanae), Bagre catfish (Ictalurus dugesii), Charal (Chirostoma chapalae), Potosi pupfish (Cyprinodon alvarezi), Flatjaw minnow (Dionda mandibularis), Black lyre (Poecilia latipinna), Graceful priapella (Priapella bonita), Chapala chub (Algansea popoche), Scowling silverside (Chirostoma aculeatum), and Largetooth silverside (C. arge).

Endemic amphibians include Rana megapoda, R. montezumae, and a near-endemic salamander genus, Ryacosiredon. The freshwater habitats also support a distinctive and endemic invertebrate fauna, including La Medialuna crayfish (Procambarus roberti), La Medialuna shrimp (Palaemonetes lindsayi), and the Crayfish's obligatory parasite, La Medialuna ostracod (Ankylocythere barbouri).

Threats
The freshwater species of this largely xeric region compete with agriculture and burgeoning human populations for the limited water supply. Water withdrawals and diversions for agriculture, combined with pollution from industrial waste, agriculture, and urbanisation threaten the quality and quantity of water available to the freshwater biota of this ecoregion.

Of great concern is the tapping of aquifers (that threaten the survival of several spring fish), invasive aquatic plants (e.g., water hyacinth, Eichhornia crassipes), and introduced nonnative fish like blue tilapia and Oreochromis aureus.

Resources
• NationalGeographic.com