Nile tilapia (Oreochromis niloticus) in brackish and marine environments of the State of Rio Grande do Sul: impact of the 2024 flooding tragedy in Southern Brazil

We detected the first occurrence of Nile tilapia (Oreochromis niloticus) in the brackish and marine ecosystems of Rio Grande do Sul, the southernmost state of Brazil, following the catastrophic floods that impacted the region in the fall of 2024. We conducted seven beach surveys from the Tramandaí Lagoon inlet, extending 80 km north and 50 km south. These surveys were carried out using a four-wheel-drive pickup truck traveling at speeds up to 40 km/h, with 2–4 observers scanning the entire beach from the wash zone to the base of the dunes. For every 10 km of beach surveyed, we performed transect walks of 1 km in length. A total of 188 specimens were found stranded up to 80 km north of the Tramandaí Lagoon inlet. Oreochromis niloticus can be managed under controlled conditions with restrictions, subject to specific regulations according to the official list of invasive exotic species in the State of Rio Grande do Sul. The escape of this species from aquaculture facilities and recent records (post-2019) in Tramandaí Lagoon underscore the need to establish a long-term monitoring program for invasive exotic species in the Tramandaí River Hydrographic Basin and to improve measures to prevent escapes.