The seemingly innocent tilapia filet, a dinnertime staple for environmentally aware consumers, may no longer be the best choice at grocery markets in Asia. Scientists from the Wildlife Conservation Society (WCS) and other groups suspect that tilapia introduced to the streams of the Fiji islands may be gobbling up the larvae and juvenile fish of several native species of goby, which use the streams to spawn.

A member of the cichlid family of fishes from Africa, tilapia has become one of the most important kinds of farmed fish, due in part to its rapid growth rate.

“Many of the unique freshwater fishes of the Fiji islands are being threatened by introduced tilapia and other forms of development in key water catchment basins,” said Dr. Stacy Jupiter of WCS, who is examining the effects of human activities on Fiji’s native fauna. “Conserving the native fishes of the islands will require a multi-faceted collaboration that protects not only the waterways of the islands, but the ecosystems that contain them.”

Jupiter recently co-authored a paper published in Aquatic Conservation: Marine and Freshwater Ecosystems. Other authors include Ingrid Qauqau of WCS, Aaron P. Jenkins of Wetlands International-Oceania, and James Atherton of Conservation International.

The research team surveyed the denizens of 20 river basins on the major islands of Vitu Levu, Vanua Levu, and Taveuni. In addition to catching and identifying fishes with gill and seine nets and looking for invasive species like tilapia, the scientists rated other environmental factors. These included the potential for erosion due to loss of forest cover and riparian vegetation, road density near rivers and streams, and the distances and complexity of nearby mangroves and reefs.

The team found that streams with tilapia contained 11 fewer species of native fishes than those without. Native species like the throat-spine gudgeon, the olive flathead-gudgeon, and other gobies turned out to be the first to go. An absence of forest cover adjacent to streams also resulted in fewer fish species.

Based on the study results, the researchers recommend that remote and undeveloped regions on the three islands, where waterways shelter a full complement of native species and no tilapia, should be considered priority locations for management. They also recommend the forests around these waterways should be conserved.

“Protecting the native freshwater fish of oceanic islands takes more than simply managing isolated rivers and streams,” said Dr. Caleb McClennen, director of WCS’s Marine Program. “A holistic conservation approach is needed, one that incorporates freshwater systems, the forest cover which surrounds them, and the coastal estuaries. And keeping invasive species out of natural habitats is a key component to effective management.”

For more information, read the press release: Trouble in Paradise (the Fishy Kind) as Introduced Tilapia Dine on Native Fish Fry