This study reports on the ingestion of microplastics by the alien fish Pirapitinga, Piaractus brachypomus (Characiformes; Serrasalmidae) that escaped Vembanad lake, the largest brackish water lake in the south-west coast of India, from the aquaculture systems during flooding. Microplastics separated from the gut of 32 out of the 123 fishes (26%) examined were identified using Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR), and Raman Spectroscopy. In total, 69 microplastic particles, represented by fibers, foam and fragments were recovered from the fish, with sizes ranging from 0.89 to 4.85 mm. The ATR-FTIR spectral analyses revealed the presence of polymers polyethylene and Nylon 6. The occurrence of PP, Nylon 6, PET and PBT were confirmed using Raman spectroscopy. The presence of MPs in the gut content of alien fish P. brachypomus could be a reflection of the increasing microplastics pollution in the estuaries and backwaters along the south-west coast of India.