Abstract
Sterile triploid Atlantic salmon (Salmo salar) show inconsistent seawater grow-out, but the reason why remains unclear. The purpose of this study was to determine the salinity optima of triploid post-smolts. Diploids and triploids were assessed for smoltification status during an underyearling smolt regime before being transferred to one of four different salinities, 0, 11, 23 and 35 ppt at 12 °C and under 24 h continuous light for 83 days. During this period, fish growth, plasma biochemistry, and production traits (vertebral deformities, ocular cataracts, sexual maturation) were monitored. Molecular biomarkers in the gill (nkaα1a, nkaα1b, nkcc1a) suggested triploids reached peak smolt earlier than diploids and began the desmoltification process before the start of the salinity treatments, however this was not reflected in gill Na+/K+-ATPase enzyme activity. At the initiation of the salinity treatments triploids were significantly larger than diploids (mean weight g ± SE: 71 ± 0.7 and 87.2 ± 0.8 for diploids and triploids, respectively) and there was a ploidy effect on post-smolt growth, with body weight showing a clearer positive trend with salinity in diploids (0 < 11 = 23 = 35 ppt) than in triploids (0 < 11 < 35 = 23 ppt) (final mean weight g ± SE: 255.2 ± 7.4, 303.9 ± 9, 313.9 ± 9 and 342.4 ± 12 for diploids and 322.9 ± 9.7, 361.7 ± 10.7, 425.9 ± 12.1, 415.2 ± 12.2 for triploids at 0, 11, 23, and 35 ppt, respectively). Plasma Na+ and Cl− increased, but plasma pH decreased, with increasing salinity in both ploidy. However, ploidy only had transient effects on plasma biochemistry depending on the salinity treatment. There was no ploidy effect on vertebral deformities (21% of both ploidy had one or more deformed vertebra). In contrast, triploids had a significantly higher prevalence of ocular cataracts (84 vs 98% in diploids and triploids, respectively) with a higher mean cataract score (mean ± SE: 1.93 ± 0.1 and 2.78 ± 0.1 for diploids and triploids, respectively), but a significantly lower prevalence of pubertal male post-smolts (15 vs 2% in diploids and triploids, respectively). Salinity treatment had no effect on vertebral deformities, cataracts, or post-smolt sexual maturation. In summary, there was a ploidy mismatch for smoltification biomarkers in the gill and salinity had a strong effect on post-smolt growth, but the effects were ploidy dependent.
Highlights
Norway has been trialling the use of sterile triploid Atlantic salmon (Salmo salar) in commercial facilities to prevent genetic in teractions between farm escapees and wild fish (Stien et al, 2019; Madaro et al, 2021)
At the initiation of the salinity treatments triploids were significantly larger than diploids and there was a ploidy effect on post-smolt growth, with body weight showing a clearer positive trend with salinity in diploids (0 < 11 = 23 = 35 ppt) than in triploids (0 < 11 < 35 = 23 ppt)
Salinity treatment had no effect on vertebral deformities, cataracts, or post-smolt sexual maturation
Summary
Norway has been trialling the use of sterile triploid Atlantic salmon (Salmo salar) in commercial facilities to prevent genetic in teractions between farm escapees and wild fish (Stien et al, 2019; Madaro et al, 2021). The technology and the production methods for large-scale triploid production have been available for several decades, they are rarely used in the commercial production of Atlantic salmon due to concerns regarding their farm performance. Considering their sterile nature and energy re-allocation, early predictions were that triploids would outperform diploids, espe cially during the reproductive seasons. Triploids will often show lower seawater growth compared to diploids (Fraser et al, 2013) The reasons behind this inconsistency are most likely multiple and probably result from the physiological differences between diploids and triploids, such as differences in temperature optima (Sambraus et al, 2017, 2018) and nutritional requirements (Fjelldal et al, 2016). Only Tasmanian (Australia) has used triploids as a fraction of the com mercial production as a backup to diploid production that suffers from extreme seasonal highs of pre-harvest sexual maturation (Amoroso et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
