Water temperature and oxygen: The effect of triploidy on performance and metabolism in farmed Atlantic salmon (Salmo salar L.) post-smolts

The use of sterile triploids in Atlantic salmon aquaculture would mitigate the environmental risks associated with introgressive hybridization between escaped farmed and wild Atlantic salmon. However, production of farmed triploid salmon is limited due to reports of poorer growth and higher mortality when compared to diploids, in particular under sub-optimal environmental conditions. To address these concerns, we monitored triploid and diploid Atlantic salmon post-smolts at temperatures between 3 and 18 degrees C and 100% oxygen saturation (O-2 (sat)), and additional periods of 60% O-2 (sat) (hypoxia) at 6 or 18 degrees C, respectively. Feed intake and oxygen consumption rate were monitored throughout the experimental period. Muscle and blood samples were collected at 100 and 60% O-2 (sat) at 6 and 18 degrees C for analysis of white muscle energy phosphates (creatine phosphate, adenosine triphosphate) and carbohydrate fuels (glucose, glycogen) as well as blood clinical chemistry (whole blood: hematocrit; plasma: Na+, K+, Cl-, glucose, lactate, pH, triacylglycerol). Mortality was similar between ploidies, but higher in triploids compared to diploids during reduced O-2 (sat) at 18 degrees C. Compared to diploids, triploids had higher feed intake (% biomass) at <= 9 degrees C, but lower feed intake at >= 15 degrees C. Feed intake peaked at 12 and 15 degrees C for triploids and diploids, respectively. Triploids progressively reduced feed intake with increasing temperature after peak feeding, indicating reduced scope for specific dynamic action with increasing water temperature. During hypoxia, triploids had lower feed intake than diploids at 6 and 18 degrees C. The difference in feed intake was not associated with any ploidy effect on body weight gain or feed conversion ratio, but triploids had greater body length growth compared to diploids. At >= 15 degrees C triploids consumed less oxygen than diploids. In the white musculature, the only observed difference between ploidies was a lower level of glycogen in triploids compared to diploids at 18 degrees C and 100% O-2 (sat). In the blood plasma, the concentration of ions was lower and glucose level higher in triploids compared to diploids at 18 degrees C and 60% O-2 (sat). The results of this study indicate that triploid Atlantic salmon post-smolts can substitute diploids, but are less tolerant to high seawater temperature and low O-2 (sat). For sea-cage farming of triploid salmon post-smolts, this would favour production areas with maximum temperatures of 15 degrees C and sufficient oxygen. Statement of Relevance: This study demonstrates that triploid Atlantic salmon post-smolts have lower temperature optima for feeding and growth than diploids, a similar physiological response to high temperatures, but higher mortality under suboptimal conditions. Consequently triploid Atlantic salmon post-smolts may be well suited for commercial farming in geographical regions with moderate water temperatures in the summer and autumn months. (C) 2017 Elsevier B. V. All rights reserved.