VERIFYING THE REPRODUCTIVE POTENTIAL OF TRIPLOID FARM ATLANTIC SALMON

The Atlantic salmon is a keystone species for natural ecosystems and human communities, but wild stocks have declined by ~90% to their lowest recorded levels. One cause of this collapse is salmon farming, the world's fastest growing form of food provision. At least 95% of Salmo salar on our planet are now reared in farms, but hundreds-of-thousands escape each year to the wild. These escapees can survive, disperse hundreds of miles, enter wild spawning populations, and ultimately reproduce. Farm fish are different to wild salmon, having been intensely domesticated since the 1970s for rapid growth and feed conversion in cages. If they reproduce with wild salmon, farm fish erode and disrupt wild-adapted gene pools, causing ecological destabilisation through loss of important locally-adapted traits like disease resistance, phenology and growth. This impact from aquaculture is described by the BBSRC-NERC call as 'the most controversial contemporary issue in Atlantic salmon farming.' Big numbers of farm fish have been found in some wild salmon spawning populations, and evidence from across the Atlantic shows that rivers near farms have had the greatest wild salmon declines, by about 50% each generation.

We propose to scientifically test and verify a potential solution to the problem of farm x wild reproduction: triploid sterilisation. Triploid induction of just-fertilised fish eggs, by applying pressure to cause retention of the second set of maternal chromosomes, produces fish that are likely to be reproductive dead-ends. Triploidy is routinely applied in trout farming, to prevent stocked fish from introgressing non-native ecosystems. Although triploid fish try to spawn, gametogenesis in most species is usually disrupted and females are often sterile. However, triploid induction does not necessarily sterilise males. Detailed studies on plaice and tench reveal that triploid males produce fully motile sperm that can fertilise haploid eggs almost as effectively as sperm from diploid equivalents. It is therefore essential that triploidy is fully verified in both sexes of a species, including under sperm competition, before we can be confident that triploid males pose no reproductive threat to wild salmon spawning populations. Even if triploids cannot produce viable offspring, large numbers of escapes could impact on wild fish by 'occupying' eggs and sterilising the reproductive potential of wild females. We will therefore fully evaluate the reproductive function of triploid farm Atlantic salmon, thereby proving biosecurity.

We know that male triploid salmon show normal breeding behaviour, can induce females to spawn, and release milt. However, information on the fertilisation and reproductive potential of triploid salmon is lacking. The only scientific study of triploid adult Atlantic salmon reproduction examined just a single male, showing that it was fertile but its offspring had poor survival. We will therefore conduct detailed scientific trials on triploid male fertility, using established techniques that measure sperm and egg performance in a range of relevant conditions to assay triploid reproductive function. We will trial the performance of triploid males in sperm competitions (both in vitro and between competing males), because the salmon mating pattern is naturally promiscuous. Our experiments will generate meaningful results that will allow a full and detailed assessment of the reproductive impact of triploid farm salmon when they escape into wild spawning populations.

The salmon farming industry is now in a position to embrace triploidy, since research reveals that triploids can perform as well as diploids under the right farm and diet conditions. Triploid salmon are just starting market trials, so our project is perfectly timed to assess this solution to farm x wild introgression. We will ensure that our research achieves impact, by disseminating findings to the public, policy-makers, NGOs, and salmon farmers.

Ample evidence shows that huge growth in Atlantic salmon farming has damaged wild salmon populations. One source of impact is the loss of hundreds-of-thousands of farm salmon each year, which enter wild spawning populations and reproduce. Farm salmon, having been intensely domesticated, are phenotypically and genetically very different to wild fish. Introgression of wild populations with farm traits therefore erodes and dilutes essential local wild adaptations; experimental and comparative research shows this leads to ecological disruption and serious depression of wild productivity.

We will experimentally verify a solution that could prevent escaped farm salmon from reproducing. Triploid induction, where hydrostatic pressure retains the egg's second polar body, generates maternal triploids which suffer reproductive compromise. Although female triploids are invariably sterile (effectively blocking invasion by alien exotics), effects on males differ greatly between species, and some retain near-normal fertility and can have reproductive impacts even if aneuploid sperm yield low offspring survival.

Triploid male Atlantic salmon can fertilise ova, show normal breeding behaviour, release milt, and induce females to spawn, but no detailed experimental work has been conducted on the fertilisation capacity of farm triploids to impact on wild populations of their own species. We will evaluate triploid male reproductive function using techniques that measure sperm form, function and performance, in a range of relevant conditions with different wild strains, and under in vitro sperm competitions and between competing males. Our experiments will generate results allowing a full and detailed assessment of the reproductive impact of triploid Atlantic farm salmon when they escape into wild spawning populations. We now know that triploid salmon perform as well as diploids in aquaculture, so this experimental verification of reproductive potential is especially timely.

The United Nations and World Bank see major growth in aquaculture being essential for satisfying global food demands, but important questions about sustainability exist. This project will address the significant and complex issue of introgression into wild populations by fish carrying domesticated genotypes.

Atlantic salmon farming is important in aquaculture, of huge economic value to the UK and Norway, and a significant employer and generator of economic growth in rural areas. Despite this success, farming has grown at a cost to the environment via impacts on wild salmon, which have their own significant economic, ecological and societal value. This situation creates conflict, and our research will answer key questions about a solution to this conflict: Does triploid sterilisation solve the problem of farm escape reproduction? Answering this question using rigorous science will provide objective evidence to allow more responsible management and protection of important natural and farmed resources. The research team has good records of pro-active societal engagement from their research, including dissemination to media, society, government, NGOs, and the aquaculture industry, and we will build on these in this project.

The work will impact on two main groups:
1. WILD SALMON INTEREST GROUPS, who are concerned about farm introgression from salmon escapes damaging wild populations. They include a large body of economically important anglers, significant for tourism in rural communities, and who have strong influence through organisations like the Atlantic Salmon Trust and the Atlantic Salmon Federation. Also relevant are those who depend upon wild fisheries for traditional sustainable harvest, such as stake and bag netters around Scotland, as well as commercially important wild salmon fisheries. More broadly, the intrinsic natural heritage value of wild salmon as a keystone species is something that many people and NGOs hold highly.
2. FARM SALMON INTEREST GROUPS comprise all elements within the aquaculture industry, and indirect beneficiaries such as national governments who gain significant export income. Scientific evaluation of triploid sterility by an independent team will provide an important opportunity for this industry.

Impact will be achieved primarily by communicating research findings through an active network of media engagement, NGOs, national authorities, and salmon farmers. In addition to this dissemination, we plan four routes to achieve impact:

1. THE ATLANTIC SALMON TRUST (AST) is a respected NGO encouraging research to promote wild salmon conservation. Its forte is being 'able to punch well above our weight in terms of influencing politicians and regulators'. The AST works closely with the Rivers and Fisheries Trusts of Scotland so engaging with both will allow impact to flow through these powerful lobby groups. We propose two milestones in this relationship:
(a) A symposium on 'Solutions to resolve differences between wild and farm Atlantic salmon interests', involving relevant scientists, the latest research findings, and participation from a wide range of end-users, including salmon farmers.
(b) CASE partnership with the AST on a complementary PhD project to link with UEA's NERC/BBSRC DTPs.

2. THE NORTH ATLANTIC SALMON CONSERVATION ORGANISATION is a key international conservation body, and we will attend their annual meeting to present results and engage directly with end users.

3. THE AQUACULTURE STEWARDSHIP COUNCIL's main mission is to '...transform aquaculture towards environmental sustainability...'. Should our results indicate effective triploid sterilisation, we will lobby the ASC to include triploidy as a standard within its highly influential ASC certification standards for salmon farming.

4. AQUA GEN LTD is the major farm salmon breeder; we will attend a meeting at their HQ in year 2, to present our findings to a core provider of farm fish to the aquaculture industry.