Changes in water temperature and oxygen: the effect of triploidy on performance and metabolism in large farmed Atlantic salmon

Abstract

In salmon farming, the use of sterile triploids (3N) can mitigate the problem of escapees interbreeding with wild salmon. However, triploid salmon appear less tolerant to high water temperatures and low oxygen levels compared to diploids (2N). To investigate how the thermal performance and physiology of large (2.5 kg) triploid Atlantic salmon Salmo salar L. differs from those of diploids, both ploidies were subjected to water temperatures between 3 and 18°C. The fish were exposed to reduced oxygen saturations (O 2 sat , 70%), termed hypoxia, at 6 and 18°C. Triploids fed more than diploids between 3 and 9°C and at similar levels at 12°C. At 15°C, the feed intake significantly dropped in both ploidies, although more in triploids. During hypoxia, feed intake was higher in triploids at 6°C and equal to diploids at 18°C. The overall feed conversion ratio was similar between ploidies. Muscle energy phosphates were generally lower in triploids than diploids, while muscle glucose, blood haemoglobin and haematocrit were lower in triploids than diploids at ≥12°C. Plasma lactate levels tended to be higher in triploids and increased with increasing temperature and at hypoxia in both ploidies. Plasma cortisol increased in both ploidies at high temperatures and was highest in triploids under hypoxic conditions at 18°C. Triploids had a higher cataract score at the start of the experiment and developed more cataracts throughout the experiment. The present findings show that large triploid Atlantic salmon perform better at colder water temperatures compared to diploids and differ in parts of their physiological expression at increasing and high temperature.

Differences in metabolism of triploid and diploidSalmo trutta f. lacustrisunder acclimation conditions and after exposure to stress situations

“…These morphometric differentiations may be considered as a compensation mechanism finally resulting in similar haemoglobin concentrations between the ploidy levels. The present data are in accordance to a study on O. mykiss and S. fontinalis (Benfey & Biron, ), while reduced haemoglobin concentrations were reported in peripheral blood of triploid S. salar (Graham, Fletcher, & Benfey, ; Sambraus et al, ) and O. tshawytscha (Bernier et al, ).…”

“…However, at 19°C triploids could not metabolize phosphocreatine and regenerated ATP slower than diploids (Hyndman, Kieffer, & Benfey, ). In adult triploid Atlantic salmon ( S. salar ) muscle energy phosphates were generally lower than in diploids (Sambraus et al, ). Additionally, muscle glucose and blood haemoglobin concentrations were decreased at elevated temperatures (Sambraus et al, ).…”

“…In adult triploid Atlantic salmon ( S. salar ) muscle energy phosphates were generally lower than in diploids (Sambraus et al, ). Additionally, muscle glucose and blood haemoglobin concentrations were decreased at elevated temperatures (Sambraus et al, ). In brown trout ( S. trutta ) metabolism was similar in response to exhaustive exercise between triploids and diploids at 10 and 19°C suggesting that triploids tolerated stress in a similar way as diploids (Preston et al, ).…”

Triploidy affects standard and postprandial metabolism in brook charr,Salvelinus fontinalis

“…Despite these advantages, triploidy has yet to become widely adopted in salmon aquaculture because in stressful environments (e.g., high temperature, hypoxia, and exhaustive exercise), triploids perform poorly compared to their diploid counterparts (Hyndman et al 2003a;Hansen et al 2015;Sambraus et al 2017a;Sambraus et al 2018). Therefore, many studies have attempted to find physiological differences between triploids and diploids, as pinpointing such differences could allow for aquaculture practices to compensate for them.…”

“…A possible explanation for why triploidy influences performance is that fundamental changes in their cell size and number (Benfey 1999) affect metabolic processes under suboptimal conditions to a greater extent than in diploids. For instance, while numerous studies have not found a significant effect of triploidy on standard or routine metabolic rates (SMR and RMR, respectively) at or near optimum temperatures for diploids (Sezaki et al 1991;Parsons 1993;Hyndman et al 2003b;Bernier et al 2004;Lijalad and Powell 2009;Bowden et al 2018), experiments conducted at higher temperatures suggest that triploids have a lower thermal optimum for metabolism than diploids (Atkins and Benfey 2008;Sambraus et al 2017a;Sambraus et al 2018). Routine metabolic rate is the metabolic rate of a fish in a post-absorptive state that is experiencing routine (but minimal) periods of activity; RMR is distinguished from SMR in that measurements taken during minor activity are included, whereas SMR involves protocols to exclude periods of significant activity (Chabot et al 2016a).…”