Boundaries

This ecoregion encompasses the Chao Phraya basin, which is a major river of central Thailand that flows through Bangkok to the Gulf of Thailand. The southeastern border extends to include the Bang Pakong basin, Thailand.

Terrestrial habitats

This ecoregion comprises a number of terrestrial ecoregions, including the Kayah-Karen montane rain forests, Central Indochina dry forests, Northern Thailand-Laos moist deciduous forests, Luang Prabang montane rain forests, Chao Praya freshwater swamp forests, Southeastern Indochina dry evergreen forests, Chao Praya lowland moist deciduous forests, Cardamom Mountains rain forests, and Indochina mangroves (Wikramanayake et al. 2002).

Description of endemic fishes

This ecoregion contains around 30 endemic species, largely in the Cyprinidae and Balitoridae families. For example, some Schistura species such as S. deansmarti, S. dubia, S. menanensis, S. pridii, and S. spilota are endemic to the Chao Phraya basin. Another endemic is Platytropius siamensis, which was restricted to the Chao Phraya and Bang Pakong basins, but is now considered to be extinct (IUCN 2012; Vidthayanon 2005).

Justification for delineation

For Southeast Asia, delineations were determined using a bottom-up approach that employed both published and unpublished field data and expert assessment (Abell et al. 2008; Kottelat 1989). The ecoregion contains subterranean systems in northern Thailand and Phitsanulok that are inhabited by endemic cave fishes and crustaceans. There is also a large swamp in Bung Boraphet. The floodplain is very heavily impacted by urban, industrial and agricultural development and several species are considered extinct (M. Kottelat pers. comm. 2006).

The Nan River basin was included in of this ecoregion since it contains fauna basically identical to the Chao Phraya region. However, it also contains several genera that are otherwise only known from the Mekong basin (Sectoria, Hemimyzon) and species whose closest relatives are in the Mekong basin and not in the Chao Phraya basin (in the genera Oreoglanis, Onychostoma, Rasbora, Schistura, Rhinogobius), reflecting an earlier connection with the Mekong basin (M. Kottelat pers. comm. 2006).

Level of taxonomic exploration

Although this is among the first areas for which aquatic biodiversity data became available in South East Asia, Chao Phraya should still be considered as under-surveyed. In addition, many species new to science have been observed in recent years (M. Kottelat pers. comm. 2006).