30 DECEMBER 2023 • WORLD AQUACULTURE • WWW.WAS.ORG Norwegian Food Safety Authority has now suspended any further licenses for farming triploids at sea from 2023 onwards. The production reports from 2020-2023 will form a basis as to whether triploid Atlantic salmon have any future in the Norwegian industry. Where Next? To date, the commercial trials have highlighted two predominant issues with triploids. The first is that smolt timing has a large effect on their performance. The second is they are more susceptible to diseases, such as ISA and Parvicapsula. Smolts in Norway are being released into seawater throughout the year. This is a large shift away from the industry’s foundations when smolts were only released in the spring following the natural development of seawater tolerance during a biological process called “smoltification.” However, early results suggest triploids smoltify earlier than expected when produced “out-of-season,” but this does not happen when using natural spring smolts (de Fonseka et al. 2022). Therefore, the poor performances of triploid autumn and summer smolts may be because these fish have passed the opportune moment to transfer them to sea. Unfortunately, this has not been assessed in the commercial trials with farmers using diploid protocols and smolt quality being assessed purely based on how many fish survive the first months after transfer. There is no biological data on whether or not triploids in these trials were actually “ready” to be transferred. Are triploids immunocompromised? Anecdotal reports from sea-cages commonly find this, but tank studies consistently find little effect of triploidy on disease susceptibility. This includes ISA (Aunsmo et al. 2022). Similarly, triploids are often anecdotally regarded as being more easily stressed than diploids, but again, tank studies of acute stress provide little evidence for it (Fraser et al. 2012). This may simply be because fish find it easier to live in experimental tanks as the environmental conditions are often very stable and close to optimal. This is unlike the sea-cage environment, which is highly dynamic with fluctuating salinity, temperature, and oxygen saturation, all of which frequently may go outside the optimal range for extended periods of time. To date, we know little about how triploids cope under such fluctuating conditions, but in general, conditions outside the optimal leave fish weaker and more open to getting sick or stressed. Have We Given Triploids a Fighting Chance? One of the key takeaways from the triploid experience is the inherent diploid bias in all the current projects. Triploids are always treated the same way as diploids. This is understandable given they are still the same species, but it may also be limiting our ability to assess their true potential. Genetics, handling procedures, vaccines, farm locations, the timing of sea transfer, and feed are all optimized for diploid biology. Even after the advice on triploid nutrition was given, many experiments still give triploids feed designed for diploids (Madaro et al. 2021). In addition, the largescale commercial trials have no controls. Only 2 out of the 54 triploid groups have a diploid reference group from the same egg supplier, locality, and sea water transfer time (Stien 2019, 2021a, b). Even then, they were kept at different densities. The rest of the triploid groups were compared to diploids which were produced by different parents, in some cases from different suppliers so from completely different strains, transferred to sea at different times of the year, kept at different densities in different numbers of cages, and/ or slaughtered at different times. There is also no guarantee, even when sharing a locality and year class, that they experience the same number of handling events, such as more or less lice treatments, which can also have a dramatic effect on performance. Because of these differences, it is challenging to pinpoint how to move forward. Conclusions Norway has spent considerable resources on assessing the feasibility of using triploid salmon. It’s clear the technology exists to reliably produce them en masse but using them now with current farming practices would most likely lead to a significant drop in the welfare of Norwegian salmon. Unfortunately, we are not sure why. To solve this there needs to be more cooperation between scientists and farmers to perform more rigorous comparisons. We also need to better understand the basic requirements of triploids, and not simply compare them to diploids. This is a mammoth effort, and it’s unclear whether this can be done before newer technology is available for producing sterile salmon, such as GMO’s or vaccines. The only example of a commercial company focusing specifically on the needs of triploid salmon is AquAdvantage, but these are also transgenic and only grown indoors under entirely artificial environments where triploids generally perform well anyway. In contrast, Tasmania has been using triploids in commercial sea-cage production for several decades and farming them in conditions not recommended by researchers in Norway: warm areas. However, reports/open access data on their performance is hard to find and there has been little knowledge shared between the two regions. Currently, we await the results of the review into triploid welfare by the Norwegian Food Safety Authority, which is due in 2024. This will determine whether they have any realistic future in Norway. Right now, there appears to be no quick fix to the significant problems we have already encountered in sea-cages. Triploids do perform well in experimental tanks, but we have few producers growing market size fish indoors in Norway. Due to these problems, the egg supplier AquaGen AS recently removed triploids from their online catalogue. But Benchmark Genetics Iceland is still supplying them to Greig Seafood Newfoundland for use in Canada where they have started to be stocked in Placentia Bay as of 2022. Here, triploids are being used out of necessity rather than choice. Greig was only given permission to farm Norwegian strains in Canada if they were sterile (Newfoundland and Labrador Regulation 2018). In Norway, we await the results with interest. Notes Thomas W. K. Fraser*, Per Gunnar Fjelldal and Tom J. Hansen, The Institute of Marine Research, Matredal, 5984, Norway. * Corresponding author: thomas.fraser@hi.no References Aunsmo, A., L. Martinsen, T. Bruheim, M.M. Sekkelsten-Kindt, A. Sandtrø, S. Gaasø, S. Braaen and E. Rimstad. 2022. Triploid Atlantic salmon (Salmo salar) may have increased risk of primary field outbreaks of infectious salmon anaemia. Journal of Fish Diseases 45: 1733-1743.
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