The present study was carried out to investigate the species diversity and population structure of freshwater fishes of six wetlands (also called Bird Sanctuaries) of Uttar Pradesh viz., Patna, Nawabganj, Sandi, Lakh Bahosi, Saman and Sur Sarovar. The sampling was done from three years period 2017 to 2020. The results of present investigation revealed the occurrence of twenty fish species in all the study areas belonging to four orders viz. Cypriniformes, Mastacembeliformes, Perciformes and Siluriformes and 11 families i.e. Cyprinidae, Cobitidae, Nemachilidae, Mastacembelidae, Channidae, Osphronemidae, Heterorpnuestidae, Sisuridae, Bagaridae, Chichlidae and Ambassidae. In all the study wetlands Cyprinidae was found to be dominant (35%), Osphronemidae (20%), Mastacembelidae, (10%), followed by family Cobitidae, Nemacheilidae, Channidae, Sisuridae, Bagaridae, Heterorpnuestidae and Ambassidae showed least contribution of 5% each. The fish diversity indices i.e. Shannon weiner (H) and Evenness (e) at all the six wetlands were 1.31, 0.9084 & 0.5710, 1.2068 & 0.6202, 1.0961 & 0.6117, 1.1552 & 0.4649, 0.9080 & 0.5068, 1.3002 & 0.6682 at wetlands viz, Patna, Nawabganj, Sandi, Lakh Bahosi, Saman and Sur Sarovar respectively.

Most of the species recorded in the present study were under 19 Least Concern (95%) and 1 species namely Chagunius chagunio were found to be under Near Threatened Category (5%) of the International Union for Conservation of Nature (IUCN).