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Mozambique tilapia (Oreochromis mossambicus) is an invasive fish species illegally introduced into Australia during the 1970s. Tilapia have since spread rapidly — partly due to the movement of fish between water courses by humans, and they are now found in many locations throughout eastern Queensland and in Western Australia.
In late 2003, Mozambique tilapia were found near Herberton on the Atherton Tablelands, 66 km southwest of Cairns in North Queensland. Individual fish were recovered from the larger of two weirs, which is the source of Herberton’s water. These weirs are located on the headwaters of Wild River in the Herbert River catchment. This catchment is the largest in the Wet Tropics bioregion and drains into coastal wetlands of high conservation value in the Hinchinbrook/Ingham area.
To assess the extent of the tilapia infestation at Herberton, Queensland fisheries researchers conducted electrofishing surveillance in early 2004. Almost 1000 fish were removed, most of which were juveniles1. No further surveys or control measures were undertaken. By late 2004, tilapia were found to have spread about 500 m downstream into the second weir in the system. Following this discovery, the Department of Agriculture, Fisheries and Forestry (DAFF) held a meeting with the former Herberton Shire Council to discuss the threat that tilapia posed to the greater Herbert River catchment if they were to escape from the weirs. In 2006, with Council support, DAFF and the Invasive Animals Cooperative Research Centre (IA CRC) initiated a trial electrofishing program to remove Mozambique tilapia from the weirs.
DAFF conducted the initial electrofishing operations in 2003 and 2004. Intensive electrofishing control efforts between 2006 and 2011 were supported by the IA CRC, with the approval of the former Herberton Shire Council, now Tablelands Regional Council (TRC).
Management options available to stop the spread and/or eradicate Mozambique tilapia from the weirs were limited. Completely draining the weirs or applying fish poisons were not feasible due to the weirs’ use as a drinking-water supply. As an alternative, a research program was initiated to control the population of tilapia by physically removing the fish through monthly boat-mounted electrofishing. The cost of this control method was estimated to be about AUD $27 600 for each of the three years of the study’s duration.
The main feature of this program was the use of electrofishing, a technique for collecting fish from freshwater systems2 commonly used by scientists to collect data on fish populations. Electrofishing works by passing an electrical current (usually pulsed direct current) through water to create an electrical field.
The current can be produced either by a battery (using a backpack unit) or a generator (bankmounted or boat-mounted unit). This sampling technique is not suitable for use in a marine environment as the fish have a lower conductivity than the surrounding saltwater (see More Info).
Boat-mounted electrofishing units send an electrical current into the water via trailing wires attached to poles (anodes), which extend from the front of the boat. The boat hull then acts as a cathode and completes the circuit. As the boat travels through the water, any fish within a few meters of the anode wires are drawn towards the front of the boat (electrotaxis) and subsequently stunned (electronarcosis). Stunned fish float to the surface where they are collected using a large dip net. Fish quickly recover once removed from the electrical field. Data such as length and weight are recorded before the fish are released unharmed, or in the case of pest fish, humanely euthanised.
Electrofishing as a management and control tool has some important limitations. It is:
In the short term, regular electrofishing appears to have halted the spread of Mozambique tilapia from the Herberton weirs into the greater Herbert River catchment. Targeted electrofishing removal has resulted in the tilapia population now being dominated by juvenile fish. Integration of control methods such as gill netting, trapping and/or native predator introduction will be needed to achieve full eradication of Mozambique tilapia in the weirs.
Thuesen PA, Russell DJ, Thomson FE, Pearce MG, Vallance TD and Hogan AE (2011). An evaluation of electrofishing as a control measure for an invasive tilapia (Oreochromis mossambicus) population in northern Australia. Marine and Freshwater Research 62:110–118.
PestSmart Toolkit for Tilapia
Invasive Animals Ltd has taken care to validate the accuracy of the information at the date of publication [August 2013]. This information has been prepared with care but it is provided “as is”, without warranty of any kind, to the extent permitted by law.