Background. The East Kolkata Wetlands in India (a Ramsar site) are sewage-fed, nutrient-rich water bodies successfully used for fish production. The vermiculated sailfin catfish, Pterygoplichthys disjunctivus (Weber, 1991), exotic to India, has invaded these wetlands. The management and control of this catfish has been hindered, because of the lack of information on its abundance, population structure, biological traits, level of establishment, and competition with native fish species. Materials and methods. Within 2013–2015 studies were carried out on the population structure of P. disjunctivus, its food habits, reproductive biology, and initial impacts in the wetlands through monthly and seasonal collection of samples, examination of food items, reproductive parameters, catch data, and gathering fishers experience. Results. The length (TL) and weight of the specimens ranged from 10 to 55 cm and from 120 to 1250 g, respectively. Major food items of the catfish were detrital matter (%IRI 56), unidentified plant matter (%IRI 11), fish eggs (%IRI 11), polychaete worms (%IRI 5), and other minor items (%IRI 0.3 to 4). At 50% similarity, the food items of P. disjunctivus overlapped with that of Macrognathus pancalus, Channa punctata, Nandus nandus, Anabas testudineus, Clarias batrachus, Oreochromis niloticus, Cirrhinus mrigala, and Cyprinus carpio while at 80% it overlapped with that of C. mrigala and C. carpio. The fecundity of P. disjunctivus, in the wetlands, was the highest recorded for the species. Females attained the first maturity at 24 cm TL and reproduced multiple times within July–November. The breeding period of the species overlapped with 13 native fish species, of which it seriously overlapped with that of Gudusia chapra, Amblypharyngodon mola, Pethia conchonius, P. ticto, N. nandus, C. punctata, and A. testudineus. The sailfin catfish has established reproducing populations in the wetlands and reached ‘invasive’ proportions constituting 4.83% (300.04 t · year–1) of the mean annual fish catch (6203.85 t · year–1) from the wetlands. The invasive risk assessment showed a high risk of the species in the current scenario and probable climate change scenarios in future in the region. Conclusions. Pterygoplichthys disjunctivus has successfully colonized the sensitive East Kolkata Wetlands, which might easily spread to neighbouring water bodies including the sensitive Ganga River and Sundarban mangroves and cause ecological and economic disturbance unless preventive measures are taken as the species has high invasive risk in the region.@en