Texas harbors 191 species of native freshwater fishes, 89 of which are considered imperiled. Five fish species are considered likely extinct from the state, while another six are considered extirpated, meaning they no longer exist in Texas but still occur in other areas of their native range, such as in adjacent U.S. states or Mexico. Declining freshwater fish diversity is a conservation issue not unique to Texas. Freshwater fishes are threatened throughout North America and currently have the highest extinction rate among vertebrates (7.5 extinctions per decade since the 1950s). Of the 1,213 freshwater fishes found in North America, 39 species and 18 subspecies are considered extinct. Similar to other areas of the continent, the primary cause of fish imperilment in Texas is alteration of freshwater systems (e.g., groundwater extraction and concomitant reductions in spring discharge, river fragmentation, alteration of natural river flow patterns, degradation of water quality, the introduction of non-native species), which continues to occur at rates and scales that threaten the long-term persistence of native freshwater fishes.
Read more here from Tim Birdsong, Deputy Director, Inland Fisheries Division, TPWD