More non-native fish species than natives, and an invasion of Malawi cichlids, in ancient Lake Poso, Sulawesi, Indonesia

Ancient Lake Poso in Central Sulawesi, Indonesia, is among the deepest lakes in Asia, and hosts a largely endemic fauna of fishes, crustaceans, and molluscs. Introduction of non-native fish species started at least a century ago to foster local fish production. Recent fieldwork suggests that introduction of non-native fishes is ongoing, including species that originate from the ornamental pet trade. These include the hybridogenic ornamental “flowerhorn” cichlid, a fish that spread rapidly in Sulawesi’s Malili Lakes, and the “golden cichlid,” Melanochromis auratus from African Lake Malawi. This popular aquarium species colonized Lake Poso even more rapidly than the flowerhorn, and is omnipresent at benthic habitats across most of the lake. Here, we list records of 17 non-native fish species from Lake Poso, present the first assessment of golden cichlid stomach contents outside of their native habitat, report the occurrences of non-native crustaceans, molluscs and plants, and discuss potential impacts on the native fauna and ecosystem. Most of the non-native species have established substantial populations, and it appears very plausible that the non-native fauna affects endemics. This is supported by the finding that golden cichlid stomachs contained a broad spectrum of items, including fish, their scales, fins, eggs and larvae, and various invertebrates. We conclude that non-native species introduction poses a substantial and increasing threat to the Lake Poso fauna, a major hotspot of aquatic biodiversity in the Wallacea region.