Animal Health and Welfare
Triploid (sterile) salmon - animal health and welfare
Report no: 2023:22
Fish health and welfare is generally reduced in sterile triploid farmed Atlantic salmon than traditional salmon in aquaculture. This can partially be mitigated through dietary supplements and by environmental adjustments, such as water temperature.
This is the key message in a review on fish health and fish welfare for triploid Atlantic salmon under commercial conditions.
This report was conducted by VKM on behalf of the Norwegian Food Safety Authority.
The use of sterile farmed salmon has been suggested as a potential solution in reducing the risk of escapees impacting the genetic integrity of wild populations. One way to achieve sterility is by making the fish triploid, meaning that the egg receives three sets of chromosomes instead of two (which is the current standard for salmon aquaculture at present).
VKM has reviewed the scientific literature, including peer-reviewed articles and other relevant reports, to assess fish health and welfare in triploid salmon under commercial farming conditions. This review report was written by a project group with expertise in salmon biology aquaculture systems, veterinary medicine, fish health and fish welfare, virology, bacteriology, parasitology, breeding and genetics.
Triploid salmon are often found to have poorer fish health and welfare than diploid counterparts, under commercial farming conditions. These fish are, for example, more prone to skeletal and heart deformities, cataracts, more susceptible to skin ulcers, and cope less well with stressful events and handling.
-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, says Espen Rimstad, Chair of the VKM project group.
Rimstad adds that the optimum temperature range may be lower for triploid salmon, based on findings from experimental studies. Data also indicate that triploids are more prone to experience hypoxia at higher water temperatures. Other observations in cages or field data point towards more susceptibility to infections by infectvious salmon anaemia (ISA) or ulcer development due to the bacterium Moritella viscosa.
-Triploid salmon appear to be less robust at higher temperatures than traditional diploid salmon, and have other nutritional requirements, especially regarding phosphorous and histidine, according to Rimstad.
-Therefore, triploid salmon require different operative conditions. 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, says Rimstad.
Uncertainties and data gaps
Some of the conclusions are uncertain, due to inconsistencies in the results from various field and experimental studies. Uncertainties can also be attributed to limitations in study design, with regards to various health- and welfare aspects, when comparing triploid with diploids.
There are data gaps in understanding factors such as impact of early environmental conditions, temperature tolerance, interactions between ploidy and genotypes and other genetic parameters.
This review report has been approved by the VKM Panel on Animal Health and Welfare.