Aquaculture  - Biotechnology topics

The Triploid Approach

Salmon farming is the largest sector in Canada’s growing aquaculture industry. One of the challenges facing Atlantic salmon aquaculture development, however, has been preventing farmed fish from escaping into the wild. The worry on both the east and west coasts, is that the escaped salmon will interbreed with wild salmon, which could alter the genetic makeup of these stocks as well as their ecological interactions.

One technique being looked at to address these concerns is the use of triploid salmon (see also ‘Biotechnology to help Protect British Columbia’s Wild Salmon Stocks – the All-Female Approach’), i.e., salmon with three sets of chromosomes (the threads of DNA that carry genetic information) instead of the normal set of two. The extra set of chromosomes prevents development of viable eggs or sperm so, if the triploid fish escape, they can’t reproduce. Triploid salmon are occasionally found in wild and cultured populations, and are relatively easy to mass produce.

What is the issue?

One problem with triploid salmon is that some show deformities, such as lower jaw defects, slower growth and higher mortality than their normal (diploid) relatives. This has tended to discourage the aquaculture industry from using triploid salmon.

DFO researchers and their partners are working to discover the cause(s) of these undesirable traits, in order to find ways to fix or minimize them. Because triploid salmon may escape, scientists will also assess how triploid salmon perform under wild environmental conditions, e.g., do they show mating behaviour or competition for other resources.

The research plan

Researchers think that triploids have more defects because their nutritional requirements may be different than those of diploid salmon. They are, therefore, studying the total energy, protein, fat, mineral and vitamin profiles that maximize the health of triploids and minimize physical abnormalities.

The two types of salmon may also require different growing conditions in order to thrive. For example, triploids don’t do well under low oxygen and high temperature conditions, which may be found in aquaculture operations. Scientists will, therefore, compare the performance of the two types of salmon under varying temperatures, oxygen levels, salinity and pH levels. Because salmon spend part of their lives in freshwater hatcheries and part in salt water, these experiments will cover both fresh and salt water conditions.

Researchers will also look at the effects of triploid salmon on wild salmon populations. While the likelihood of spawning interactions is believed to be low, triploids could also affect wild salmon populations by competing with them for food and habitat.

Benefits of this research

While positive results from this research should reduce concerns over risks of escapee farmed Atlantic salmon, it will also:

Enhance the conservation and biodiversity of Canada’s wild salmon stocks by preventing the introduction of non-local stocks into the wild gene pool;

Increase Canadian confidence in salmon aquaculture that uses farmed fish that cannot compete genetically or ecologically with wild salmon stocks; and,

Provide Canadians with a safe and readily available food source.