Dietary phosphorous and protein supplementation enhances seawater growth and reduces severity of vertebral malformation in triploid Atlantic salmon (Salmo salar L.)

Diploid (2N) and triploid (3N) sibling post-smolts were divided between six sea pens and fed: a standard commercial nutrient package diet (2×2N SP, 2×3N SP), or an iso-energetic nutrient boosted (higher dietary protein and phosphorous) package (2×3N BP) until market size. 3N groups initially grew significantly faster than 2N, and by harvest, 3N BP weighed significantly more (3210±87g) than 2N SP or 3N SP (3007±64g; 2965±88g), while there was no significant difference in weight between ploidy in SP diet. Higher visible vertebral (9.6±0.4%) and jaw deformities (10.6±1.2%) were observed in 3N compared to 2N (0.9±0.1%; 1.3±0.5%). However, x-ray radiography revealed that 3N BP and 2N SP had comparable levels of severely affected individuals at time of sea transfer, while 3N SP showed a 3 fold increase in the severity of malformed individuals. The tail region (R3) in 3N SP fish had both the lowest vertebral strength and stiffness and the highest number of deformed vertebrae. Fillet quality attributes were comparable between diet and ploidy. These findings show that triploid growth rate can be sustained until harvest throughout the seawater phase, and more importantly the progression of spinal deformity beyond that at sea transfer can be stabilised by increasing dietary P during the marine phase. Tailored triploid specific aquafeeds must be formulated to support growth and prevent deformity in order to minimise welfare implications and allow exploitation of faster growth potential of triploid salmon within industry. •Triploid Atlantic salmon growth rate can be sustained during marine rearing using protein enriched diets•Severity of skeletal deformity can be reduced by feeding nutrient enriched diets•Occurrence of skeletal deformity in triploid Atlantic salmon must be addressed during freshwater stages in the first instance