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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 (O2 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. © The authors 2018. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are unrestricted. Authors and original publication must be credited.

Increased swimming speed of Atlantic salmon is generally considered an improvement to welfare under aquaculture settings, as group structure is improved and agonistic behaviour reduced. As such, establishing fish farms in exposed areas with fast water current velocities should be favourable. However, at some locations, velocities exceed what is known as preferable for salmonids, and this may compromise fish welfare. In this study, behaviour and fin erosion were observed on post-smolt salmon stocked at 39 kg m−3 in raceways at 3 water current velocities: fast (1.5 body lengths [BL] s−1), moderate (0.8 BL s−1) and slow (0.2 BL s−1). Movements that affect group structure and interactions between individuals varied by up to 20-fold between velocities. A behavioural change occurred directly after velocities were set. Severe fin erosion decreased over time in all groups, but new injuries increased almost 3-fold in the faster-velocity group. Our results suggest that moderate velocity is ideal from a welfare perspective. At slow velocity, higher frequency of structural movements and between-individual interactions could be stressful for the fish. At faster velocity, the fish have to focus on swimming, which could increase unintentional collisions with obstacles and other individuals and result in new fin erosion. Our results suggest that management of water currents may be an effective way of controlling behaviour and may thereby improve welfare. © The authors 2016. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are unrestricted. Authors and original publication must be credited.

The current paper compares the use of adipose fin and muscle biopsies as non-lethal sampling procedures, and the suitability of triacylglycerol (TAG) versus total lipid (TOT) fatty acid composition (fatty acid methyl esters, FAME) to estimate dietary history in farmed and wild matur- ing Atlantic salmon Salmo salar. TAG FAME gives best resemblance to dietary history. Fatty acid composition differs between tissues, and sample series should preferably be from 1 tissue only. TOT FAME supplies informative data on dietary history in fatty tissues, but differs from TAG FAME when total lipid levels are low. The reason is a larger contribution of phospholipid FAME. In wild maturing salmon, lipid content in adipose fin and muscle is low. TAG provides good data on dietary history, while TOT is less informative. Escapees are well identified analysing 18:2n-6 and 18:3n-3 fatty acids, which are high in commercial feed. For estimating a wider range of dietary history after escape (switch to wild prey), or feed preferences in wild fish, other fatty acids have to be taken into account. This requires the use of multivariate methods, like principal com- ponent analysis. Adipose fin and muscle biopsies are good alternatives for non-lethal sampling using the TAG method. The minimum amounts of samples to be used are proposed to be 0.5 to 1 g of adipose fin and 60 to 100 mg of muscle. The method of storage (liquid nitrogen/dry ice) does not affect fatty acid compositions. Other tissues can also be used for fatty acid profiling. Snout is a good alternative, being lipid-rich even in wild fish with low muscle lipid.

Escapes of farmed fish from coastal farms around the world are believed to have genetic and ecological consequences for wild fish populations. Each year there are numerous escapes of adult farmed Atlantic salmon Salmo salar. However, survival until maturity appears to be low. One possible explanation is that many of these salmon have difficulties switching to live prey. To address this possibility, growth rate and dietary preference were recorded in recaptured salmon released in 3 groups from August to October 2008 within a small fjord in south-western Norway (Masfjord). The fish were primed with a commercial diet containing 11% of the 'vegetable oil marker' 18:2n-6 before release. In the 14.5 to 35.1% of fish recaptured, growth rates were generally good (0.21-1.23% d -1 of fish recaptured in main fjord >2 mo after release), with body weight doubled or more for fish recap- tured after 19 wk and thereafter. However, fish recaptured in a small arm of Masfjord (Hopsvag) had a growth rate close to zero and were in poor condition. While stomachs of recaptured fish were gen- erally empty in the first weeks after release, pellets from fish farms were found in more than 80% of the stomachs after 12 wk and thereafter. Additionally, the level of 18:2n-6 in depot lipids (11% of fatty acids) of the muscle indicated that none of the fish recaptured the following autumn and winter in the vicinity of the release site had switched to wild prey diets. Salmon that escape during autumn are unlikely to compete for prey with wild fish in the vicinity of the release site.