Aquaculture  - Biotechnology topics

One of the challenges aquaculture faces is preventing farmed fish from escaping. Such escapes are not only an economic loss to the farmer, but have raised questions and concerns over the risk the farmed fish pose to wild counterparts. Since Atlantic salmon are not native to British Columbia (BC), concerns there include risks to the genetic makeup of wild pacific salmon populations through interbreeding, as well as establishment of feral populations (escapees that survive in the wild) that could compete with other fish for food and other ecological resources, such as shelter, spawning beds, etc..

There are two possible options for addressing these concerns over escapee risks. The first is development of triploid salmon (see fact sheet: ‘Biotechnology to help Protect Wild Salmon Stocks – The Triploid Approach’). Because triploid salmon possess three sets of chromosomes, rather than the usual two sets, they are unable to produce viable eggs or sperm. So, if they escape, they can’t reproduce with wild salmon or establish competitive feral populations. The second option is development of all-female strains of Atlantic salmon.

What is the issue?

Normal females of most species, including salmon, have two X-chromosomes (XX), and males have one X and one Y (XY) chromosome. However, ‘sex-reversal’ technology can be used to produce reproductively functional male salmon with an XX-chromosome profile. When a normal XX-female is mated with a sex-reversed XX-male, all their offspring are XX-chromosome females.

The problem with this approach is how to be sure that the XX-males are really XX and not normal XY-males (that would produce both male and female offspring if used as broodstock). Genetic testing would provide that certainty, but it is hard to do in salmon, because the sex-determination region in a salmon’s DNA is small and hard to find.

To help solve this problem, researchers at Fisheries and Oceans Canada (DFO) are working to develop a Y-chromosome DNA probe for Atlantic salmon. A DNA probe is a tool, based on target sections of DNA (such as the sex-determination region), that ‘lights up’ when it comes into contact with a matching DNA sequence in a tissue sample. Researchers aim to produce a probe that will ‘light up’ when it finds the DNA sequence specific to the Y-chromosome, thereby showing if sample is from an XY-male, rather than a sex-reversed XX-male.

The research plan

Researchers are using a variety of biomolecular techniques to isolate DNA sequences present in male Atlantic salmon, but absent from females. Such sequences will be used to develop the tool to detect genetic sex of an Atlantic salmon. These tools will allow results to be determined quickly and without killing the fish, since samples of blood or small clips of fin tissue are all they require. The scientists will verify the reliability of each test by comparing their results with those using traditional, time-consuming methods of determining genetic sex (i.e., mating the males to females and seeing if they produce any male offspring, indicating the male has the Y-chromosome ). Once a reliable Y-chromosome probe is developed, researchers will partner with industry to develop monosex female populations of Atlantic salmon for use in aquaculture.

Benefits of this research

If this research is successful, it will benefit the Atlantic salmon aquaculture sector on Canada’s West Coast by:

allowing aquaculture operations to establish all-female populations of Atlantic salmon;
 
ensuring that Y-chromosome male Atlantic salmon are not accidentally used in aquaculture;

removing the risk of feral Atlantic salmon establishing populations off the BC coast; and,

contributing to environmentally sustainable Atlantic salmon aquaculture production in BC.