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The Lake Malawi/Nyasa catchment contains over 835 endemic cichlid fish species. This unique biodiversity has made it widely recognised as one of the world's most significant freshwater ecosystems. Here we report the first occurrence records of two invasive tilapiines, Oreochromis niloticus and Oreochromis leucostictus, inside the Lake Malawi catchment. The introductions took place during initiatives to develop aquaculture and new capture fisheries. Oreochromis niloticus is an important competitor and predator of native species, has potential to hybridise with indigenous Oreochromis species, and has been widely implicated in biodiversity loss globally. It was a key contributor to the destruction of the Lake Victoria indigenous Oreochromis fishery. In light of apparent risks to unique biodiversity, and in the absence of robust evidence that introductions will bring enhanced socio-economic benefits over indigenous …