Ploidy effects on hatchery survival, deformities, and performance in Atlantic salmon (Salmo salar)

The production of sterile triploid Atlantic salmon (Salmo salar) may help address the increasing pressure on the industry to reduce potential breeding between farmed escapees and wild fish populations. However, many previous studies have observed poor performance at sea in triploid stocks (growth, survival, and deformity). This may result from poor early hatchery performance and a strong parental effect. Therefore, in the present study, two year classes (2007 and 2008) of mixed sex fish were created (10 males:10 females) to examine ploidy interactions on hatchery performance. Egg batches were divided in two at fertilisation with one group subjected to a hydrostatic pressure shock to induce triploidy. Triploid rate was confirmed at 100% in all groups, verified by red blood cell nucleus length measurements. Survival to hatch did not differ between ploidy. However, reduced survival was found to strongly correlate with gamete quality. During the hatchery phase ploidy significantly affected size at hatch, with diploids generally larger than triploids. Growth advantage of diploids over triploids was only maintained for 6 weeks post-first feeding, with triploids generally out-growing their diploid siblings by the end of the hatchery phase. Deformity prevalence in first feeding stages was generally low (mean < 2%), with no overall effect of ploidy. Our findings show that triploid salmon can perform as well if not better than their diploid siblings. The low incidence of deformity during the hatchery and freshwater phases is also a significant improvement over previous reports in triploid salmon stocks.