Triploid farmed salmon generally have poorer health and welfare than traditional farmed salmon.
That's the key finding published by the Norwegian Food Safety Authority (Mattilsynet), in a report summarizing knowledge about triploid salmon for potential commercialization by the Norwegian fish farming industry.
Triploid salmon, which are unable to reproduce because they have three sets of chromosomes instead of the usual two, have been trialled in Norway since 2013.
The salmon were considered a possible solution to reduce the risk of farmed fish escapes impacting on wild salmon populations. To produce triploid salmon, the fish eggs are induced to have three sets of chromosomes.
In Norway, 30-35 million triploid salmon were produced as part of testing and documentation of commercial triploid salmon production over a 10-year period. All of the salmon in the trials are now due for slaughter and disposal by December this year.
In other countries, triploid salmon are already in commercial use, for example, U.S. land-based salmon farmer AquaBounty has commercialised its own strain of triploid salmon, "AquAdvantage" salmon, which were the first genetically engineered animals approved for human consumption in the United States and Canada.
However, in the case of AquaBounty, the triploid salmon are farmed in land-based facilities rather than sea-based net pens. The Norwegian research focused on triploid salmon grown in traditional net pen conditions.
The Norwegian report published on 1 November shows that triploid salmon suffer from a range of health problems which makes them "unsuitable for commercial farming under current industry conditions".
The report, carried out by Norway's Science Committee for Food and Environment (VKM) on behalf of Mattilsynet, will be used to give formal recommendations on the viability of farming triploid salmon to the Ministry of Trade and Fisheries.
The report authors found that triploid salmon are more prone to malformations in the skeleton and heart, as well as more likely to develop cataracts and skin ulcers.
Through both direct observation and field data, the researchers also established that triploid fish are more susceptible to infections such as infectious salmon anemia (ILA) virus and bacterial wound infection from the bacterium Moritella viscosa.
On the welfare front, triploid salmon are also less tolerant to stress and handling, the researchers found, as well as less robust to higher water temperatures than traditional salmon. Different farming conditions would therefore be needed for this type of fish, including different nutrition.
"Most scientific studies conclude that triploid and diploid salmon do not differ significantly, in terms of oxygen consumption, oxygen binding capacity, and aerobic swimming capacity, at temperatures considered optimal for diploids," said report lead author Espen Rimstad.
However, Rimstad added, "Triploid salmon appear to be less robust at higher temperatures than traditional diploid salmon, and have other nutritional requirements, especially regarding phosphorous and histidine."
"Research has shown that many of these fish health and welfare issues can be mitigated, if conditions are optimized for triploids. However, some of the necessary adjustments are not feasible under the present commercial farming conditions," Rimstad said.
The report's conclusion, Mattilsynet said, "corresponds to the Norwegian Food Safety Authority's experiences and assessments from inspections."
"The VKM report will be important when the Norwegian Food Safety Authority must give our professional assessment to the Ministry of Trade and Fisheries as to whether this is a method that sufficiently safeguards fish welfare in accordance with the current regulations," said Inge Erlend Næsset, Director of Regulations and Control at the Norwegian Food Safety Authority.