Using environmental DNA as a tilapia surveillance tool
Invasive species are a major problem in Australian waterways, especially in the tropics where warmer water favours the many tropical species found in the aquarium trade (the main source of fish introductions). The Ross River, which runs through the city of Townsville in North Queensland, has more invasive species than any other river in Australia. At the last count, 20 species of exotic fish had established in this river, tilapia being the most problematic.
Spotted TilapiaTilapia, a member of the Cichlidae family, were introduced to Australia as aquarium fish. They have been slowly spreading across Queensland, and are now present in 21 of the 76 catchments, and are considered the most problematic invasive fish across the state. Their success lies in their highly efficient breeding strategies and flexible habitat and dietary preferences. They tolerate a wide range of temperatures, high salinities and low levels of oxygen and are also very aggressive, easily out-competing and displacing native Australian fish. It is therefore vital to prevent their further spread into new catchments. This goal relies upon a combination of public education (not to spread the fish) and early detection of any newly created populations to guide management responses, including eradication attempts where feasible.
Early detection, and understanding the distribution of nascent populations are key to deciding upon appropriate management responses for new incursions. Researchers within Centre for Sustainable Tropical Fisheries and Aquaculture (CSTFA) and TropWATER have developed field and laboratory methods for the application of eDNA to assist tilapia management. This work was recently showcased in the popular ABC TV programme Catalyst (‘Tilapia’ aired on 6th November 2014).
The first step was to develop primers specific to tilapia. Primers are very short genetic sequences from a standard part of the genome and are used to distinguish DNA in a water sample the way a supermarket scanner distinguishes products using the black stripes of the barcode. As no two species have the exact same ‘code’, the primers are species-specific. The research team have been developing cheap and rapid means of collecting, filtering and analysing water samples, as well as doing experimental work to verify detection probabilities under a range of varying conditions (e.g. temperature, salinity, flow, time since tilapia were present).
- eDNA technology is used by the research team for both early detection and management of tilapia by:
- detecting their presence where they have been reported
- determining their distribution and map high risk areas
undertaking routine surveillance in these high risk areas
The technique has a high reliability of detection and has been used to elucidate the distribution of tilapia in the Mitchell, Townsville, Fitzroy, and Pioneer catchments in Queensland, and a recent incursion into northern New South Wales.
The TropWATER team are currently working on developing primers for another potentially problematic invasive pest species, the climbing perch (Anabas testudineus).