Allodontichthys polylepis

Allodontichthys polylepis is a small freshwater fish endemic to the Lerma River basin in central Mexico. This species belongs to the family Goodeidae, a group of livebearing fish found exclusively in Mexican highland waters. The fish inhabits shallow areas of rivers and streams with moderate current flow, typically in areas with rocky or sandy substrates and aquatic vegetation. As a goodeid, it exhibits internal fertilization and gives birth to live young rather than laying eggs. The species has experienced severe population declines due to multiple anthropogenic pressures affecting its limited range. Habitat degradation represents the primary threat, with urban development, agricultural expansion, and industrial activities altering water quality and flow patterns throughout the Lerma basin. Water pollution from domestic sewage, agricultural runoff, and industrial discharge has significantly impacted water chemistry in many areas where the species historically occurred. Additionally, water extraction for human use has reduced flow levels in many tributaries. The introduction of non-native fish species has created additional competitive pressure and predation risks. Climate change may exacerbate existing stressors through altered precipitation patterns and increased temperatures. Conservation efforts for this critically endangered species remain limited, though some Mexican institutions have initiated research programs to better understand population status and ecological requirements. Habitat restoration and water quality improvement initiatives in the Lerma basin could benefit this species, but coordinated conservation action is urgently needed to prevent extinction.