The effect of triploidy on juvenile Atlantic salmon (Salmo salar) response to varying levels of dietary phosphorus

Although triploidy induction is a reliable method for producing sterile fish for aquaculture and fisheries management, little is known about how triploidy influences nutrition and bioenergetics of fish. The aim of this study was to determine whether triploidy affects nutrient uptake and body composition in fish, using juvenile Atlantic salmon (Salmo salar) as the test species and varying the levels of dietary phosphorus. Triplicate groups of sibling triploids and diploids (45 g initial weight) were fed isocaloric diets with 0.76, 0.99 and 1.39% total phosphorus in a 12-week growth trial, followed by a feed digestibility trial with diets having 0.67, 0.93 and 1.15% total phosphorus. Triploids had a higher growth rate and lower condition factor than diploids during the growth trial, with no difference in feed conversion ratio. Whole-body lipid and energy levels, as well as nitrogen and energy efficiency ratios, were higher in the triploids, but ash and moisture levels were lower. Triploids initially had lower plasma phosphorus levels than diploids, but on the final sampling day there was no difference between ploidies in levels of plasma phosphorus, bone ash and phosphorus within the bone ash. Apparent digestibility coefficients for phosphorus, ash and dry matter were not significantly different between triploids and diploids. The observed effects of triploidy on growth and body composition therefore cannot be attributed to phosphorus utilization and metabolism.