| Résumé | Full-sibling, size-matched ‘all-fish’ growth hormone transgenic (TG; gene construct EO-1α) and non-transgenic (NTG) Atlantic salmon (Salmo salar L.) comprised of conventional diploid (DIP) and reproductively-sterile triploid (TRIP) fish were fed the same experimental grower diet in freshwater until they tripled their weight. The study was conducted to provide baseline data on growth performance, feed efficiency, nutrient digestibility, skeletal disorders, bone ash content and bone mineral composition of NTG/DIP, NTG/TRIP, TG/DIP and TG/TRIP fish and to determine if a practical grower diet for conventional NTG/DIP Atlantic salmon requires modification for TG/TRIP fish. TG fish consumed a significantly higher amount of feed on a daily basis but due to enhanced growth rates, better feed conversion ratios and higher nitrogen retention efficiency they achieved target weight gain in a considerably shorter period (40%) than NTG fish. Total feed required to produce the same fish biomass was reduced by 25%; representative of a significant reduction in overall feed intake. Of TG fish, TRIP had some significant effects on production traits primarily due to lower feed intake relative to DIP fish. Although feed intake was lower in TG/TRIP fish, feed efficiency, digestibility and nutrient retention efficiencies were equal to those of TG/DIP fish and, without exception; TG/TRIP fish out-performed their conventional NTG counterparts, regardless of ploidy. TG/DIP and TG/TRIP fish demonstrated a higher cellular capacity to direct dietary non-protein energy towards satisfying their daily metabolic energy requirements, allowing for a higher proportion of dietary amino acids to be directed towards protein biosynthesis; rather than catabolised as a dietary energy source. Since dietary protein is the largest and most expensive component of salmon feeds and also the major source of nitrogenous pollution from salmon farming, this could represent a highly beneficial alteration of energy metabolism which could result in more economical and ecologically-sustainable Atlantic salmon aquaculture, especially when conducted in closed-containment land-based systems. Although bone ash content of TG fish was slightly lower than NTG fish, no significant differences in key bone mineral composition were observed and the occurrence of skeletal disorders was low (< 4%), regardless of transgenics or ploidy. |
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