New techniques, new diets being tested for triploid fish
The potential for interbreeding between escaped farmed salmon and their wild counterparts has been a public relations quagmire for some sectors of the global aquaculture industry. Now Norwegian fish farming companies are raising one million sterile salmon in sea cages in an effort to mitigate the issue.
The sterile fish are triploids, using methods developed by Norwegian researchers funded in part by the Research Council of Norway in close cooperation with the aquaculture industry.
“If we succeed in producing sterile salmon on an industrial scale, we can substantially reduce the negative genetic impact on wild fish populations,” says Arne Herre Staveland, manager at Eide Fjordbruk, one of the six aquaculture companies participating in the experiment.
Pressure-treating eggs
Triploid salmon are produced by exposing salmon eggs to high pressure, a treatment that causes the offspring to receive the usual one set of chromosomes from its father, but two from its mother. This method was developed in the 1980s and has been used with some success with various species around the world.
However, there have been problems with the process which can cause skeletal deformities in salmonids. Now, thanks to new knowledge gained in part from the sequenced salmon genome, the method has re-emerged as a potential solution.
“New research indicates that we can prevent the skeletal problems by modifying the diet,” explains Geir Lasse Taranger of the Institute of Marine Research in Bergen.
“Also, new molecular tools help us to better understand how triploid salmon respond to different environmental conditions, which enables us to develop better protocols for how to farm them.”
“The new research also shows that triploid makes salmon more sensitive to warmer temperatures and low oxygen concentrations,” says Dr Taranger.
“Triploid salmon appear to have different nutritional and environmental requirements than normal salmon, so we need to adapt the production methods.”
Monitored from fry to harvest
AquaGen has been supplying the pressured-treated eggs, which grew into the sterile salmon currently being put to sea. These experimental fish will be closely monitored from their fry stage until harvest.
Putting one million sterile salmon to sea is a milestone in this research. Compared to normal diploids, the triploid salmon grow faster in their freshwater stage and require a special diet with, for instance, extra phosphorous to prevent skeletal problems. If this is to succeed, it is critical that the producers adapt their production regimes to accommodate the altered traits and utilise the advantages that triploids have to offer.
The first triploid salmon will be ready for slaughter in spring 2015, so the trials can be assessed soon thereafter.
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