Gene technology to be used in carp control plan

By Graeme O'Neill
Friday, 10 January, 2003

The Murray-Darling Basin Commission is to back a radical new attempt to control Australia's worst aquatic pest, the carp Carpio cyprinus.

Chairman Dr Don Blackmore said the commission would work with the Pest Animal Control Cooperative Research Centre (PAC CRC) in a long-term project to reduce carp numbers throughout the Murray-Darling system using CSIRO-developed Daughterless gene technology.

The commission is believed to be investing around $AUD3 million in the project. The chief executive of the CRC, Dr Tony Peacock, said further funding would be sought from state fisheries departments in the eastern mainland states whose rivers are infested with carp.

The Daughterless synthetic gene construct exploits CSIRO's patented 'hairpin' gene-silencing technique to switch off a gene for an enzyme called aromatase, which normally converts testosterone to the feminising hormone oestrogen in developing female embryos.

Because fish embryos develop by default as males in the absence of oestrogen, the gene is expected to move through the Murray-Darling system's vast carp population, progressively skewing its sex ratio towards an all-male population.

Peacock said the Daughterless Carp project could take up to 50 years to reduce carp numbers to levels at which it will no longer be a pest. The gene will be introduced by 'seeding' infested rivers and waterways with huge numbers of transgenic male fingerlings carrying multiple copies of the Daughterless gene, to compete for mating rights with wild-type males.

According to Peacock, the gene is likely to move slowly through carp populations, initially producing a slow decline in female numbers before causing the carp population to crash.

The PAC CRC has contracted CSIRO geneticist Dr Ron Thresher's team at CSIRO Marine Research in Hobart to develop the technique for carp.

Thresher's group has already spent four years developing and testing the Daughterless gene construct. Last year it successfully ascertained that the technique works in zebrafish, under laboratory conditions.

Mosquito fish to be first target

The technology will initially be deployed against the tiny, short-lived mosquito fish Gambusia, another major aquatic pest whose range in the Murray-Darling system overlaps closely with that of carp.

Blackmore said that in the nearly 40 years since the carp entered the Murray River via an overflow channel in Mildura's Lake Hawthorn in 1964, the pest had spread throughout the Murray-Darling system.

Current estimates indicated that carp constitute around 90 per cent of the fish population in the basin, with recent surveys finding densities of one carp per square metre of water surface. The carp's environmental impacts include habitat damage, increased water turbidity -- which drastically reduces light penetration and ecosystem productivity in infested rivers -- and channel erosion.

Peacock said the PAC CRC was at the forefront of efforts to use gene technology to address environmental problems. It has been developing another form of anti-fertility technology, called virally vectored immunosterilisation (VVIS) to control major mammalian pests like the rabbit, fox and European house mouse.

The CRC expects to apply to the Office of the Gene Technology Regulator later this month to conduct the first contained field trial of a genetically modified virus developed to control mouse plagues in the Australian wheat belt.

Under laboratory conditions, the sexually transmitted herpes virus has achieved a 100 per cent sterility rate in female mice. The virus infects mice, and causes the female's immune system to mount an antibody attack that destroys her own eggs.

Last year the CRC achieved a sterility rate of nearly 75 per cent in two small experiments involving 11 female rabbits. Rabbits are Australia's worst feral pest.

Look for the full story of the Daughterless carp project in the February 6 print edition of Australian Biotechnology News

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