The effect of dietary energy level on growth and nutrient utilization by juvenile diploid and triploid brook charr, Salvelinus fontinalis

Triploids are used in aquaculture because they are sterile and do not undergo preharvest loss in flesh quality. Despite this advantage, they do not always perform as well as diploids when fed commercial diets. This study investigated whether differences in dietary energy utilization might explain this reduced performance. Dietary lipid levels were adjusted to supply diets with 22.7, 23.6 or 24.4 MJ kg-1 gross energy and fed to juvenile diploid and triploid brook charr. Fish were fed to satiation twice daily in a 70-day growth trial, with samples collected at days 0 and 70 for proximate composition and plasma insulin-like growth factor I (IGF-I) analysis. This was followed by a digestibility trial using the same diets to determine apparent digestibility coefficients. Triploids had lower growth rates and condition factor than diploids on all three diets, but there was no effect of ploidy on feed conversion efficiency. Triploids also had lower whole-body lipid content, but equal protein content, which resulted in lower energy content at both days 0 and 70. There was no effect of diet or ploidy on plasma IGF-I concentrations. Triploidy did not affect diet digestibility, suggesting that the reduced performance of triploids is due to a difference in metabolism and energy utilization. \ua9 2015 John Wiley & Sons Ltd.Peer reviewed: YesNRC publication: Ye