VERIFYING THE REPRODUCTIVE POTENTIAL OF TRIPLOID FARM ATLANTIC SALMON

大西洋鲑鱼是自然生态系统和人类群落的关键物种，但野生种群已下降约90%，降至有记录以来的最低水平。造成这种崩溃的原因之一是三文鱼养殖业，这是世界上增长最快的食物供应形式。目前，地球上至少有95%的鲑鱼是在农场饲养的，但每年都有数十万只鲑鱼逃到野外。这些逃亡者可以存活下来，分散在数百英里外，进入野生产卵种群，并最终繁殖。养殖鱼与野生三文鱼不同，自20世纪70年代以来，为了快速生长和网箱中的饲料转换，养殖鱼一直被密集驯化。如果它们与野生鲑鱼繁殖，养殖鱼会侵蚀和扰乱野生适应的基因库，通过失去重要的本地适应特征，如抗病能力、物候和生长，导致生态不稳定。水产养殖业的这种影响被BBSRC-NERC Call描述为“大西洋鲑鱼养殖中最具争议的当代问题”。在一些野生鲑鱼产卵种群中发现了大量的养殖鱼，来自大西洋彼岸的证据表明，农场附近的河流野生鲑鱼数量下降最多，每代下降约50%。我们建议科学地测试和验证农场野生繁殖问题的潜在解决方案：三倍体绝育。三倍体诱导刚刚受精的鱼卵，通过施加压力导致第二组母体染色体保留，产生的鱼很可能是繁殖的死胡同。三倍体在鲑鱼养殖业中被常规应用，以防止放养的鱼进入非本地生态系统。尽管三倍体鱼类试图产卵，但大多数物种的配子发生通常会中断，雌性往往不育。然而，三倍体诱导并不一定会使雄性不育。对二倍体和二倍体精子的详细研究表明，三倍体雄性能产生完全活动的精子，这种精子能使单倍体卵子受精，几乎和二倍体精子一样有效。因此，在我们确信三倍体雄性不会对野生三文鱼产卵种群构成生殖威胁之前，充分验证一个物种的两性之间的三倍体是至关重要的，包括在精子竞争下。即使三倍体不能产生可存活的后代，大量的逃逸也可能通过‘占据’卵子和使野生雌性鱼类的生殖潜力不孕而对野生鱼类产生影响。因此，我们将充分评估三倍体养殖场大西洋鲑鱼的生殖功能，从而证明生物安全性。我们知道，三倍体雄性鲑鱼表现出正常的繁殖行为，可以诱导雌性鲑鱼产卵，并释放乳汁。然而，关于三倍体鲑鱼的受精和繁殖潜力的信息缺乏。唯一一项关于三倍体成年大西洋鲑鱼繁殖的科学研究只检查了一只雄性鲑鱼，表明它是可以生育的，但其后代的存活率很低。因此，我们将对三倍体男性生育能力进行详细的科学试验，使用现有的技术来测量精子和卵子在一系列相关条件下的性能，以分析三倍体生殖功能。我们将测试三倍体雄性在精子竞赛中的表现(无论是在体外还是在相互竞争的雄性之间)，因为鲑鱼的交配模式自然是混杂的。我们的实验将产生有意义的结果，使我们能够全面和详细地评估三倍体养殖场鲑鱼逃逸到野生产卵种群时对生殖的影响。三文鱼养殖业现在可以接受三倍体，因为研究表明，在合适的农场和饮食条件下，三倍体可以表现得和二倍体一样好。三倍体三文鱼才刚刚开始市场试验，所以我们的项目恰逢其时来评估这一解决方案，以农场x野生导入。我们将通过向公众、政策制定者、非政府组织和鲑鱼养殖户传播研究结果，确保我们的研究产生影响。

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.