The Threat of Nile Tilapia
Nile tilapia (Oreochromis niloticus) is a species of fish native to Africa and the Middle East, and it has become one of the top species used in aquaculture worldwide. As a result of their extensive use in aquaculture, the species has been introduced into nonnative environments following the release or escape from fish farms. Research efforts conducted collaboratively by the Museum of Natural Science and The University of Southern Mississippi - Gulf Coast Research Laboratory have documented the recent establishment of Nile tilapia in coastal watersheds of southeastern Mississippi, and researchers consider the species to pose a significant threat to native fishes and fisheries if their populations continue to expand.
This species appears not to compete directly for food resources with native co-occurring sunfishes (e.g., bass, bream). Nile tilapia feed mainly on bottom sediments (i.e., base of the food web) and extract energy from accompanying organisms in the sediments. However, feeding at the base of the food web may indirectly force a cascading effect by altering food types and abundance at upper food web levels commonly foraged on by fishes such as bass and bream.
Nile tilapia become reproductively mature at a small size and individuals experience a fast growth rate. In addition, female Nile tilapia brood eggs, embryo and young in their mouths. This parental care assures that the majority of their eggs will survive to the juvenile stage. This strategy coupled with the fact that females may spawn multiple broods throughout their extended reproductive season may give this introduced species a competitive advantage over native fishes and allow them the capacity to proliferate in nonnative environments.
These adaptations make tilapiine fishes excellent aquaculture species, but also are the same attributes that allow them the ability to invade and become established in nonnative environments. Tilapiine fishes were erroneously considered incapable of tolerating the cooler water of wintertime Mississippi, in part justifying their use as an aquaculture species. Like other cichlid species, however, tilapiine fishes are highly tolerant to environmental stressors, and temperature tolerance has been reduced in more saline waters as is typical of coastal Mississippi.
Efforts should be consider by resource managers to evaluate the use of tilapia in an aquaculture setting in coastal watersheds as natural disasters like flooding and hurricanes can cause tilapias to enter and disperse into other habitats and drainages thus expanding the invasion. The establishment of exotic species is a leading threat to native ecosystems, with aquatic ecosystems at the highest risk. The ability to control exotic species is often hindered by reacting to negative impacts that occur during or after establishment.