Dietary effects on biomarkers of growth, stress, and welfare of diploid and triploid Atlantic salmon (Salmo salar) during parr-smolt transformation

Triploidy is induced in Atlantic salmon (Salmo salar) to produce sterile fish for genetic containment and to hinder early sexual maturation in farmed fish, but it can have unwanted negative effects on growth, health, and welfare. However, the growth and welfare of triploid fish may be improved by adjusting the rearing environment, feeding conditions and diets. This study evaluated physiological changes and used a suite of biomarkers to assess the potential impact of diet on growth and welfare of diploid and triploid salmon during the parr-smolt transformation. Diploids and triploids, held at low temperature, were fed a standard salmon feed or one with hydrolyzed fish proteins thought to be suitable for triploid Atlantic salmon. Fish muscle was collected monthly from October to December (2454–3044 degree-days post-start feeding, ddPSF) for analysis of biomarkers, and the progress of the parr-smolt transformation was monitored using a seawater challenge test. Real-Time PCR and radioimmunoassay were used to assess growth and stress response biomarkers (expression of genes of the GH-IGF axis and HSP70; cortisol concentrations), and oxidative stress biomarkers of lipids (MDA) and proteins (AOPP) were assayed. Changes in the biomarkers were related to sampling time rather than being associated with diet or ploidy, and the changes were compatible with the progression of the parr-smolt transformation. Growth and expressions of the biomarkers in triploid Atlantic salmon were similar to those of their diploid counterparts, and there was no evidence that the rearing conditions employed in the study resulted in stress responses being elicited. Overall, the physiological indicators and biomarkers employed in this study did not point to there being any dietary effects on performance and welfare of diploid and triploid salmon that were undergoing parr-smolt transformation.