Sammendrag
Background and terms of reference
Farmed Atlantic salmon (Salmo salar) that escape into the wild could interbreed with native
fish, posing a potential risk to the genetic diversity of wild Atlantic salmon populations. The
Atlantic salmon in aquaculture are diploid, meaning the fish has two sets of chromosomes.
To mitigate the genetic impact on wild populations, the concept of producing sterile triploid
farmed Atlantic salmon has been suggested as a solution. However, it is important to ensure
that the utilization of triploids in commercial farming aligns with the regulations set forth in
the Norwegian Animal Welfare Act.
The Norwegian Food Safety Authority (NFSA) requested the Norwegian Scientific Committee
for Food and Environment (VKM) to do an assessment about health- and welfare
consequences in triploid Atlantic salmon under commercial farming conditions, as compared
to diploid counterparts. VKM was also requested to describe the underlying physiological
mechanisms concerning consequences of triploidy as well as address potential measures to
reduce the negative impacts on the health and welfare of the fish.
Methods
A working group consisting of members with expertise in salmonid biology, aquaculture
systems, veterinary medicine, fish health and welfare, virology, bacteriology, parasitology,
breeding and genetics has drafted this opinion. To answer the Terms of Reference as
mandated by the NFSA, the authors addressed fish health and welfare as a unified concept
in this report. Two external experts have reviewed and provided their opinion before it was
assessed and approved by the VKM’s Panel on Animal Health and welfare.
The literature used in this work was peer-reviewed studies retrieved from a search in four
databases as well as non peer-reviewed reports. Selection of studies was conducted
independently by two members in the working group and based on predefined inclusion and
exclusion criteria.
Conclusions
Under commercial farming conditions, triploid Atlantic salmon are often found to have lower
standards of health and welfare compared to diploids. For example, field and experimental
studies have found triploids to be more prone to skeletal and heart deformities, and
cataracts, while field studies suggest that under commercial farming conditions they cope
less well with handling and are more susceptible to skin ulcers. However, research has
indicated that some of the effects of triploidy can be mitigated through specialized diets or
environmental adjustments.
There is a noticeable tendency across farm studies and experimental trials for triploid salmon
to be equal or larger in size at the end of freshwater phase, but equal or smaller in size at
the end of the seawater phase.
Most publications conclude that within what is considered the optimal temperature range of
diploids, oxygen consumption rate, oxygen binding capacity, and aerobic swimming capacity
do not significantly differ between triploid and diploid Atlantic salmon. However, findings
from experimental trials suggest a lower optimal temperature range for triploids, and data consistent across studies indicate that triploids possess lower tolerance to hypoxia at
elevated temperatures. Triploid Atlantic salmon are less robust to higher water temperatures
than diploid, and have other nutritional needs than diploids, especially regarding phosphorus,
and histidine.
There are few studies on the susceptibility of triploid salmon to infectious agents and
diseases. Field observations indicate that triploid fish are more susceptible to primary
infectious salmon anaemia (ISA) outbreaks than diploids under commercial farming
conditions at the level of the farm, and at cage level within farms that experience an ISA
outbreak. A higher susceptibility to the ISA virus would potentially affect not only the health
and welfare of the triploid fish at the farm with an outbreak but may potentially spread to
other farms. .............
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