Optimisation of trace mineral supplementation in diets for Atlantic salmon smolt with reference to holistic fish performance in terms of growth, health, welfare, and potential environmental impacts.

The aquafeed ingredient inventory is ever changing, from marine to plant based, and recently evolving to incorporate increasing amounts of low trophic, side stream and circular economy based raw materials, each one contributing with variable amounts and qualities of macro- and micronutrients. Meeting the micronutrient requirement of farmed fish for healthy and efficient growth under normal and challenging conditions is of paramount importance. In this study we run a trial based on a 2 × 4 factorial design with three replications for each dietary treatment, where Atlantic salmon smolt were fed one of 8 experimental diets supplemented with either organic or inorganic mineral premixes (copper, iron, manganese, selenium, and zinc) at four dietary inclusion levels. We saw a trend for higher growth rate in the organic mineral groups irrespective of the dietary mineral levels. Mineral digestibility was negatively correlated with increasing mineral supplementation levels for all tested minerals but Se which increased with the increasing supplementation in the inorganic and up to the 2nd inclusion level in the organic mineral groups. Increasing mineral supplementation affected retention efficiency of Zn, Mn, Cu and Fe while mineral source affected only the retention of Se which was higher in the organic mineral groups. Moreover, fish obtained higher EPA and DHA in their body and increased slaughter yield in the organic as compared to the inorganic mineral groups and corroborated that trace mineral inclusion levels play a key role on salmon fillet's technical quality. More effects from different origin and dietary inclusion levels of trace minerals were seen on fillet yield, fillet technical and nutritional quality, bone strength, skin morphology, organ mineralization and midgut transcriptome.

The effect of dietary n-3/n-6 polyunsaturated fatty acid ratio on salmonid alphavirus subtype 1 (SAV-1) replication in tissues of experimentally infected rainbow trout (Oncorhynchus mykiss).

Salmon pancreas disease (SPD) is one of the most commercially significant viral diseases of farmed Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in Europe. In this study, the potential for dietary mitigation of the disease using different polyunsaturated fatty acid (PUFA) profiles was assessed in rainbow trout. We experimentally infected fish with salmonid alphavirus subtype 1 (SAV-1), the causative agent of SPD. These fish were fed two diets with different n-3/n-6 PUFA ratio (high omega 3, 3.08, and high omega 6, 0.87). We assessed the influence of the diets on the fatty acid composition of the heart at 0 days post infection (d.p.i.) (after 4 weeks of feeding the experimental diets prior to SAV-1 infection), and sampled infected and control fish at 5, 15 and 30d.p.i. Viral E1 and E2 glycoprotein genes were quantified by two absolute real-time PCRs in all the organs sampled, and significantly lower levels of the virus were evident in the organs of fish fed with high omega 6. Characteristic pathological lesions were identified in infected fish as early as 5d.p.i., with no significant differences in the pathology lesion scores between the two dietary regimes. This study shows that decreasing the n-3/n-6 PUFA ratio in experimental diets of rainbow trout changes the fatty acid content of the fish, and is associated with reduced SAV-1 replication in rainbow trout.