In a long-term project, scientists have successfully made a ‘daughterless carp’ construct (an engineered gene). 

Background

Daughterless carp technology was developed by CSIRO and aims to control carp through biasing sex ratios towards males.  With fewer females in the population, it is predicted that this genetic technology could sharply reduce carp numbers in the Murray-Darling Basin within 20 to 30 years of release.

The daughterless carp program is part of the Murray-Darling Basin Commission’s Native Fish Strategy.  While the program is an area of relatively high-risk research, the possible benefits of such an innovative method of invasive species control have warranted its further development.

This is a very long-term project.  It was commenced by our predecessor, the  Pest Animal Control Cooperative Research Centre and the coordinating role has continued as part of this CRC's portfolio.

The vision of the daughterless carp project is to provide a sustainable option for the biological control of carp in the Murray-Darling Basin within the aims of improving overall catchment and waterway management, as well as achieving the Commission’s broad natural resource management objectives.

Technical information 

The conceptual basis of the project reflects an assessment that, over the longer term, a diminution in the number of female fish in the population will ultimately result in a reduction in population size.

Daughterless carp technology works using gene silencing. When fish
develop, all embryos start life as males (in humans they start as females). Aromatase (produced in the brain and reproductive organs) is the protein responsible for stimulating female development in carp and other fish at the embryo stage.  By silencing the production of aromatase, scientists can bias sex ratios toward male development through to adult.

The daughterless carriers have normal reproductive capacity and the gene is
heritable, so daughterless males can pass on the daughterless gene to wild type carp. This type of development is typical for other fish and amphibians, so the technology could probably be applied to other pest species.

Results 

The project has succeeded in developing a viable modified gene which has been tested using Japanese rice fish (which have a much shorter life cycle).   Breeding through three generations from an initial six neomale founders (produced from two different daughterless constructs) has shown only partial inheritance.  It has been found that aromatase expression in this species  has two different isoforms ('brain' and 'ovarian') making further investigation necessary.  Our PhD student, Megan Barney, has been good progress on sequencing the brain aromatase in carp.  Modifications to the gene construct technique have been made and will require further testing to see if inheritance has improved.

The next step is to breed up large numbers of carp containing the modified gene.  We then need to do extensive specificity trials in a PC2 facility.

The future 

Once we are certain that we have a viable and specific construct, it will take at least another five years before any daughterless carp are ready to be released into our rivers after strict and rigorous field trials.  It will then take many more years for the impact to be felt and carp populations to start to fall.

The time taken for the heritable daughterless gene to pass through a population of carp depends on the size of the population.  As there is a massive population of carp in the Murray-Darling Basin it is expected to be 20-30 years until we would see a significant reduction in carp numbers and probably 50 years until carp numbers are at an insignificant level.  Whereas in isolated coastal catchments where carp numbers are lower, the reducing effect of daughterless would be much faster.

Is it safe?

In this project, the daughterless carp genetic constructs are engineered, taken
directly from carp and simply modified - they are their own genes.   This means that they are specific to carp and cannot be functional in any other fish or animal species. 

If we were to apply the technology to other pest fish or cane toads, specific constructs would need to be engineered for them.

However, because carp have a similar sex determining and developmental pathway to other fish and amphibians, the daughterless carp technology can potentially be modified on other pest fish or pest amphibians such as cane toads.

Under the Gene Technology Act 2000 from the Office of Gene Technology Regulator, daughterless carp are considered a genetically-modified organism (a GMO) which is:

(a) an organism that has been modified by gene technology; or
(b) an organism that has inherited particular traits from an organism (the initial
organism), being traits that occurred in the initial organism because of gene
technology.

Even if a GM-carp or its descendent were to be caught by an angler after being released into the wild, it would be perfectly safe to eat.