The effect of vaccine-associated cross-stitch vertebrae pathology on growth of farmed Atlantic salmon

A field study comparing two vaccine regimes against pancreas disease (PD) was carried out in 2018 S0 year class smolts at two commercial sea cage sites in southern Norway. The fish from the same hatchery source were immunized using licensed vaccines; either a DNA PD vaccine and a hexavalent oil-adjuvanted vaccine (group A), or a heptavalent oil-adjuvanted PD vaccine (group B). The experimental design included the two fish groups reared together (15% as group A and 85% as group B) in four large hatchery tanks. These fish groups were later transferred to four production cages at two separate sea sites (two cages per site). In the absence of any notable PD prior to the pre-harvest sampling, the primary objective and outcome variables entailed evaluation of vaccine side effects and their impact on growth. The results show that vaccine and sea cage site significantly impacted prevalence and severity of a newly described pathology named cross-stitch vertebrae. Further, moderate to severe cross-stitch pathology (scores =3) resulted in significantly reduced growth.