The southeastern United States as defined here is delimited on the north and west by the Ohio and Mississippi rivers. Many fishes are widely distributed in the Southeast and occur in two or more hydrologic regions. The Southeast has about 485 known species of native freshwater fishes, representing 27 families. Total numbers of freshwater fishes and percentage imperiled by hydrographic region of the southeastern United States. No endangered or threatened species have been delisted.
Numbers represent imperiled species during years of listing activity.
In terms of ecological requirements, most imperiled species are those that live in small to large creeks and small rivers, are closely associated with clean stream-bottom substrates, or are isolated in spring and cave environments. This geographic trend is correlated with both a high level of diversity in the respective hydrologic regions and the quite localized or endemic distributions of many species. Most jeopardized species have restricted distributions, but the number of more geographically widespread species that are disappearing from large portions of their ranges is increasing. In the Southeast, fish declines are the result of the same factors that cause global deterioration of aquatic resources, primarily habitat loss and degraded environmental conditions. Aquatic resources are often resilient and capable of recovery, given favorable conditions.