Genetic impacts of escaped farmed salmon on wild salmon populations is still a big challenge to the sustainability of the salmon aquaculture industry . Farming sterile salmon would eliminate genetic interactions between farmed and wild salmon . To date, the most cost-effective and consumer-accepted method of inducing sterility is triploidisation . Triploidy involves a pressure shock to a fertilised egg, causing the retention of the second maternal polar body. The resulting fish contains two copies of DNA from the maternal line. But the use of triploids in commercial farms has been limited due to concerns over the poorer welfare triploids display compared to standard diploid salmon.
Triploids generally exhibit a dosage effect on the second maternal chromosome set that regulates gene expression. Most often this translates to an additive effect with more influence from the maternal line on the phenotype. We hypothesise that the doubling of the maternal line may cause an inbreeding effect in triploid offspring, and the heterozygosity level of the dam may explain the welfare challenges documented in triploids. Inbreeding can affect several production-related traits like growth rate, survival and developmental rate, and these negative effects could be compounded in triploids with a double maternal load.
To test this, we have followed standard diploid, standard triploid and gynogenetic diploids (individuals with two copies of maternal DNA only) from 12 half-sib families by measuring individual growth, survival, and welfare over an entire production cycle from fertilisation to harvest. A genetic sample from each fish and parent has been taken and will allow us to link individual growth and performance over time to family-level heterozygosity and explore how the maternal genetic load affects welfare.
Our findings could help the industry move toward a more sustainable production by implementing breeding programs specifically designed for triploid salmon production and help mitigate the welfare issues documented on farms at present.