Functional feeding traits and fecundity as predictors of invasive success of the introduced Nile tilapia, Oreochromis niloticus in Lake Bosomtwe, Ghana

Aquaculture-mediated introductions of Nile tilapia (Oreochromis niloticus) into environments where it is not indigenous is well documented. The establishment of a cage-aquaculture facility on Lake Bosomtwe in Ghana in 2012 led to the accidental introduction of O. niloticus. This study details the growing concerns about the potential invasiveness of the species by using morphological feeding traits to predict the ecological position and invasion potential. Fecundity and the relative abundance of the native and non-native species of fish were also assessed. The morphological dataset was constructed using 22 functional feeding traits of 87 fishes (13-15 specimens per species), while the feeding habits and fecundity were assessed using 60 fishes (10 individuals per species) and 66 mature females (9-12 individuals per species) respectively. The PCA ordination of the functional feeding traits and the food preferences indicated very little overlap among the O. niloticus and the native species. The mean fecundity of O. niloticus (470 +/- 178 oocytes) was lower than most of the native species. Compared to the year 2020 when the invasion index (The degree of invasion ranging from 0 to 1) of O. niloticus was 0.1, this study recorded values ranging from 0.31 to 0.97, with the alien species accounting for more than half of the catch composition in 73% of the sampling activities. The spread of the alien O. niloticus and the concomitant declines in the populations of most of the native species is, potentially, of high conservation concern, and it is predicted that further spread of O. niloticus in Lake Bosomtwe might drive these native populations into local extinction.

Automated summary

The establishment of a cage-aquaculture facility on Lake Bosomtwe in Ghana in 2012 unintentionally introduced Nile tilapia (O. niloticus), posing potential threats to the native species and ecosystem. This study used morphological feeding traits to assess the ecological position and invasive potential of O. niloticus, finding minimal overlap with native species. The lower fecundity of O. niloticus and its dominance in catch composition suggest a high conservation concern and the possibility of local extinction for native populations in Lake Bosomtwe.