Loricariid catfish of the genus Pterygoplichthys have been introduced in many localities around the world. They are freshwater fishes, but may also use low-salinity habitats such as estuaries for feeding or dispersal. Here we report results of a field survey and salinity-tolerance trials for a population of Pterygoplichthys sp. collected in Kerala, India. In both chronic and acute salinity-tolerance trials, fish were able to withstand salinities up to 12 ppt with no mortality; however, fish transferred to salinities > 12 ppt did not survive. The experimental results provide evidence that non-native Pterygoplichthys sp. are able to tolerate mesohaline conditions for extended periods, and can easily invade the brackish water ecosystems of the state of Kerala. In the light of results of the present study and considering the reports of negative impacts of the species in invaded water bodies, the management authorities may consider taking appropriate action and awareness programmes to prevent the spread of this nuisance aquatic invasive species in Kerala.