Pecos Gambusia (Gambusia nobilis) is a small (4 cm) fish that occurs in the Pecos River basin in Texas and New Mexico, though its distribution has been greatly restricted in recent years primarily due to the lowering of water tables and introduced species. In New Mexico, it is now mainly found on Bitter Lake National Wildlife Refuge and Blue Spring. They inhabit pools and outflows of clear, vegetated springs with high calcium carbonate levels and gypsum sinkholes. They do not do well when competitors (e.g., Western Mosquitofish [Gambusia affinis]) or predators (e.g., Green Sunfish [Lepomis cyanellus]) are present.