About 30,000 species of extant fishes are known, and approximately 12,300 species, or 41% of all fish species live in freshwater.
This diversity is extraordinary when we realize that freshwater fishes occupy less than 0.01% of Earth’s water volume (~97% is oceanic; ~3% is brackish), and that thousands of species remain to be described, particularly in the tropics. Over two-thirds of all freshwater fish species belong to the single teleost clade Otophysi (minnows, characins, and catfishes).
Unfortunately, degradation of freshwater ecosystems is severe in many parts of the world, and freshwater species are among the most endangered species. Conservation biologists and resource managers depend on accurate taxonomic information and museum collection records for prioritizing areas for protection and for making informed species-specific management policies.