Diet-habitat ecology of invasive tilapia and native fish in a tropical river catchment following a tilapia invasion

Many species of tilapia (a collection of fish species from the cichlidae family) have biological traits that make them successful invaders. While widespread herbivory has been observed in many tilapia species, knowledge on habitat preferences and tilapia interactions with native fish food webs is limited. This study used stomach contents and stable isotope analysis of spotted tilapia (Pelmatolapia mariae) and Mozambique tilapia (Oreochromis mossambicus), and stable isotopes of common native fish species to explore relationships between habitat and diet for fish food webs in the Mitchell River, northern Australia, three years after tilapia were detected in the catchment. While plant material was the most abundant item in tilapia stomachs, some also contained other items in small quantities, such as fish eggs, small shrimp, and bivalves. Macrohabitat type (in-channel (no tilapia), off-channel (no tilapia), weir (tilapia present)) was related to native fish food web structure, with weir food webs showing similarities to off-channel food webs. In-channel food webs were more constrained than weir or off-channel food webs, reflecting a more limited range of available food sources. Off-channel habitats including creeks and wetlands were most similar to weir habitats and may therefore be most at risk of colonization as tilapia spread throughout the catchment. This study clearly demonstrated that the successful rapid invasion of these two tilapia species is linked to suitable habitat with abundant food that fuels growth and reproduction. These findings increase understanding of diet related habitat use during new tilapia invasions and trophic interactions with native species.