Lice

18 BACKGROUND: Increasing reliance on non-medicinal interventions to control sea lice in the 19 Atlantic salmon ( Salmo salar ) farming industry imposes a high level of skin mucosal 20 disturbance and indirect health issues. Dietary supplementation with yeast-based MOS 21 products is widely used to support intestinal homeostasis across farmed species. Evidence of 22 their effect on skin mucosa is increasing in aquatic species but it remains inconsistent and 23 someway short of a clear contribution to sea lice management. A tank-based trial was 24 performed to test the effect of a yeast-based MOS functional compound (sMOS) on the skin 25 mucosal layer and its protective effects against sea lice ( Lepeophtheirus salmonis ). 26 RESULTS: The test compound significantly increased skin mucus (+46%) and goblet cell 27 density (+25 %) after 6 weeks of dietary supplementation when positive effects on intestinal 28 villi-length (+10.9 %) and goblet cell density (+80.0 %) were also documented. Following 29 dietary supplementation, a 16.6 % reduction in susceptibility to an acute standard copepodid 30 challenge was measured alongside an earlier increase in skin lysozyme activity widely used as 31 an index of innate immunity. 32 CONCLUSION: The study provides functional evidence that the benefits of dietary sMOS 33 reach beyond the intestine to the skin mucosa. Bolstering of the Atlantic salmon skin barrier 34 and immune functions and the resulting lower susceptibility to sea lice has the potential to 35 reduce the need for delousing interventions and the impact of non-medicinal interventions on 36 the animal’s health and welfare. 37 a key role for the C-Type lectin pathway.