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The Philippines Freshwater ecoregion contains many species of fish that can't be found anywhere else in the world. The ecoregion is unique in Asia because of the large number of fish species that have evolved from a few ancestral species to fill new habitats and new conditions over time. This land reveals a history of volcanoes erupting, ocean bays becoming freshwater lakes, and fish and crabs evolving into unique species found nowhere else on earth. Visit this ecoregion and you may encounter 50 volcanoes -- 10 of which could erupt at any time. Seven thousand islands, more than 21,000 miles (34,000 km) of shoreline, numerous rivers, swamps, and unique mountain lakes harbor fish and freshwater crabs that evolved over thousands of years from marine ancestors.
Freshwater flows from the northern Cordillera Central Mountains to the southernmost island of Mindanao. Some rivers, such as the Cotabato, Gata, and Agusan, rush for long distances. Streams and small rivers run slowly through plains and form swamps. The largest lake in the Philippines, Laguna de Bay, is shallow and close to sea level and was probably part of the ocean a long time ago. The second largest, Lake Lanao, is 2,296 feet (700 m) high in the mountains, and several rivers feed its deep basin, which supports a very productive fishery, as well as a unique group of fish found only here.
The Philippines Freshwater ecoregion supports two groups of related fish that can't be found anywhere else in the world. The vast majority of the fish species that inhabit the fresh waters of the Philippines (234 out of a total of 330) return to the sea to spawn. In Lake Lanao lives an unusual group of fish called a "species flock." All 18 of these species are thought to have evolved from one species, the spotted barb, which is widespread throughout Southeast Asia. This ecoregion is also home to 41 freshwater crab species, all of which evolved here and are found only here.
Many unique species in the Philippines Freshwater ecoregion soon could be extinct. The main reason is that people have brought alien species of fish into the ecoregion to use as a food source. But these species, such as carp and gobies, compete with and feed upon native species. The status of the species flock of Lake Lanao is uncertain, but it appears that several species may have gone extinct due to introduced species. Another problem is that too many forests have been cut down, exposing the topsoil to erosion. The erosion causes silt to flow into the lakes and streams, polluting the water for the organisms that live there.
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