Vertebral deformities in interspecific diploid and triploid salmonid hybrids.

Vertebral deformities in salmonid interspecific hybrids, some of which were triploidised, were assessed across three separate year classes during the freshwater life stage. Initially we crossed the eggs from a farmed Atlantic salmon Salmo salar with the sperm from either an S. salar, arctic char Salvelinus alpinus, or brown trout S. trutta. For S. salar x S. trutta, half the eggs were triploidised. In a second- and third-year class, the eggs from a farmed S. salar were crossed with the sperm from either an S. salar or a S. trutta, and half of each group was triploidised. In the two initial year classes, all hybrids were larger than the S. salar controls and triploid S. salar x S. trutta were larger than diploid counterparts. In the third year class, the S. salar x S. trutta were smaller than the S. salar, in contrast to the initial two year classes, although the triploid hybrids were still larger than the diploids. In the third year class we also observed a high degree of spontaneous triploidy in the putative diploid groups (between 16%-39%). Vertebral deformities were consistently higher in pressure-shocked triploids than diploids, irrespective of hybridisation, but there was no consistent effect of hybridisation among experiments. Although we are not able to explain the contrasting results for vertebral deformities between year classes, triploid S. salar x S. trutta can demonstrate impressive freshwater growth that could be of interest for future farming programs.