Wetlands play an important ecological role by providing shelter and habitat for diverse fish species, migratory birds, macrophytes and other aquatic organisms. Hydrological connectivity with the main river channel has a critical role in fish diversity and production in floodplain wetland. The present study showed the seasonal hydrological alteration on fish species distribution in Ansupa wetland, connected with tropical river Mahanadi, India. The river discharge showed a variation from 4549 cusec during lean season (April) to 204716 cusec during monsoon (August). It has been recorded that water flows/discharge above 200000 cusec only, inundate the wetland resulting in exchange of free flows of fish species and nutrients. The study period for the fish species diversity was undertaken during 2017-18. A total of 46 fish species were observed under the orders Cypriniformes (18), Perciformes (12), Siluriformes (7), Synbranchiformes (2), Cyprinodontiformes (1), Clupeiformes (1), Beloniformes (1), Osteoglossiformes (1), Mugiliformes (1), Anguilliformes (1) and Tetraodontiformes (1). According to the conservation status of the International Union for Conservation of Nature, four species Parambassis lala, Ompok bimaculatus, and Anguilla bengalensis are in the category of Near Threatened. Analysis showed that taxonomic distinctness is more during winter than the monsoon and pre-monsoon, indicating monsoon could play a significant role in the fish species recruitment through river connectivity. Climatic data was analysed for a period of 34 years and indicated that an increment of 0.20C in water temperature and average increase of 129mm rainfall at the study site. This slight increase in rainfall over the years could be one of the factors responsible for the fish recruitment in the Ansupa wetland, through river connectivity underlining the importance of flood for wetland fisheries recruitment and sustainability.