The native fish of the waterways of Fiji are battling an invasive species, one advocated by many sustainable fish farming proponents: tilapia. A new study by the Wildlife Conservation Society found that streams with tilapia contained 11 fewer species of native fishes than those without, leading to speculation that the introduced species may be feeding on the larvae and juvenile fish of native species.
“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.” – Dr. Jupiter, a co-author of the study
Tilapia has long been the poster child for sustainable aquaculture due to its rapid growth rate and its palatability as a food item, but this study highlights the dangers of unintended consequences from well-meaning actions: invasive species. The tilapia is a member of the cichlid family of fish, originally from Africa, but introduced around the world as a farmed fish, only to end up on the IUCN’s 100 of the World’s Worst Alien Invasive Species list.
The Fiji study, published in Aquatic Conservation: Marine and Freshwater Ecosystems, concerns “ecosystem-based management for conserving aquatic migratory pathways”, using Fiji as a case study. According to the authors, tropical, high islands of the Pacific have developed “unique freshwater fish faunas that are currently threatened by a range of human activities”, and this latest study found that the number of all fish species in mid-reaches of Fiji rivers are significantly affected by “loss of catchment forest cover and introductions of tilapia.”
The researchers tried to gauge the impacts of tilapia (and other human activities) on native fish species in the Fiji Archipelago by surveying the fish species of 20 river basins on the major islands of Fiji. The scientists also rated other environmental factors such as the potential for erosion due to loss of forest cover and riparian vegetation, the density of road building near rivers, the distances and complexity of nearby mangroves and reefs, and the presence or absence of invasive species such as tilapia.
In their studies, the team determined that the species which were most affected by the tilapia were the throat-spine gudgeon, the olive flathead-gudgeon, and other gobies. They found that Fiji waterways with tilapia contained 11 fewer species of natives than those without it: in places where the tilapia were not introduced, more species of native fish were present.
Researchers recommended that remote and undeveloped regions on the islands – those with waterways already containing the full complement of native species, with no tilapia present – should be considered priority locations for management, including the conservation of forests around the waterways and by keeping the tilapia out.
“Protecting marine and aquatic biodiversity takes more than managing isolated rivers or coral reefs. A holistic conservation approach is needed, one that incorporates freshwater systems, the surrounding forest cover, coastal estuaries and seaward coral reefs. As aquaculture continues to develop worldwide, best practices must include precautionary measures to keep farmed species out of the surrounding natural environment.” – Dr. Caleb McClennen, Director of the Wildlife Conservation Society’s Marine Program.