Tilapia cichlid fishes of the genus Oreochromis are invasive across the world’s tropical freshwaters. In Quintana Roo, Mexico, tilapia are now widespread, but their impacts on indigenous freshwater fauna are unclear. This thesis reports the effects of Oreochromis tilapia on native fish assemblages in Quintana Roo, following initial reports of their establishment in the 1980s and 1990s. Competitive interactions between invasive Nile tilapia (Oreochromis niloticus) and native Mayan cichlid (Mayaheros urophthalmus) were evaluated. The Nile tilapia was more active and aggressive than the native and better able to withstand the elevated temperatures and lower oxygen concentrations that negatively affected the native species. These results suggest Nile tilapia has broad tolerance of extreme environmental conditions that could favour invasive success of this species. Environmental DNA (eDNA) metabarcoding was evaluated as a tool for surveying tilapia invaded fish communities. Focussing on Lake Caobas, a positive association was found between the number of eDNA reads of a species, and the number of captures of individual species using conventional net sampling. Moreover, using eDNA it was able to sample 18 of the 20 known species from the lake, including invasive Oreochromis, while conventional netting sampled only 14 species. These findings support metabarcoding use in monitoring. To explore the impact of Oreochromis on native fish assemblages, six lakes were surveyed using conventional net sampling. Tilapia were rare, and only captured in three sampled lakes. Moreover, tilapia presence did not appear to influence native fish assemblages, instead dissolved oxygen was the strongest predictor of species diversity. In these systems, native predators may regulate tilapia abundance and promote resistance to invasion. In conclusion, it is recommended that monitoring of both invasive feral tilapia and the native fauna, while providing informed guidance during the development of aquaculture, would lower the risk to native fish assemblages of the region.
|Date of Award||23 Jun 2020|
- The University of Bristol
|Supervisor||Christos C Ioannou (Supervisor) & Martin J Genner (Supervisor)|