In order to assess the effect of dietary phosphorus (P) in reducing vertebral malformations and improving freshwater (FW) performance in triploid Atlantic salmon (Salmo salar), both triploid and ...diploid Atlantic salmon were fed three different dietary P inclusion levels (low: 4.9, medium: 7.7, and high: 9.7 g available P kg−1) from first feeding until smolt. Somatic and skeletal response was assessed at fry (~0.5 g), parr (~5 g) and smolt (~45 g) stages. Triploid parr initially grew faster on the high P diet, while groups fed low P resulted in a significantly higher weight at smolt. Image analysis of double stained Alcian blue and Alizarin red S fry revealed that low P fed triploid fish presented less well mineralised vertebrae, and significantly more malformed vertebrae in both parr and smolt stages following x-ray radiographic assessment. Triploid parr fed high and medium P had similar numbers of malformed vertebrae relative to their diploid counterparts but greater numbers than at smolt. Low P fed triploids had the highest prevalence of jaw and vertebral malformations as well as the highest number of deformed vertebrae in the central caudal vertebral region, which was more pronounced at parr than at smolt. Shorter vertebrae dorso-ventral lengths were observed throughout the spinal column (R1–R4) in parr fed low P and only in the caudal region (R3) at smolt. In parr, both ploidies showed reduced phosphate homeostasis protein fgf23 gene expression in vertebrae when fed low P diets, while triploids showed greater down-regulation of osteogenic factors (alp, opn and igf1r) between diets relative to diploids, suggesting possible greater active suppression of mineralisation and reduced osteogenic potential in triploids. No effects of diet or ploidy on gene expression were evident at smolt. Comparisons between development stages suggest early P supplementation in triploids is crucial for skeletal development. Ultimately, reducing vertebral deformities observed at smolt with higher P supplementation in triploids could contribute towards improving skeletal performance and welfare of the stocks in the marine phase.
•Feeding higher dietary P throughout freshwater significantly reduced occurrence of vertebral malformations in triploid Atlantic salmon.•Triploid growth was improved with higher dietary P within the fry to parr stages but reduced growth from parr to smolt.•Higher dietary P supplementation impeded diploid growth throughout freshwater.
Using sterile triploid salmon is of interest to fish farmers as a means to mitigate interbreeding between farmed and wild fish, prevent pre-harvest maturation and offer potential for faster growth. ...We investigated within the same experiment whether growth, deformity and cataract prevalence in diploid and triploid Atlantic salmon post-smolts (8 full-sib families) were influenced by isolated- or mixed-ploidy rearing during 12months of sea water grow-out in tanks until harvest. Diploids attained significantly higher harvest weights than triploids in both treatments (+6.7% isolated, +26.3% mixed). Triploid harvest weight was 29.6% lower under mixed ploidy rearing than their isolated triploid siblings. A similar effect was also observed in diploids (12% lower harvest weight). Family had a significant effect on harvest weight in both ploidy. However, family harvest weight in triploids showed a linear relationship between isolated and mixed rearing (r2=0.76), while a non-linear relationship was found between diploids reared in isolation or mixed populations (r2=0.88). Furthermore diploid family weight correlated positively with triploid weight in isolation (r2=0.65), but a non-significant relationship was observed under mixed rearing (r2=0.49). Diploids had a significantly higher condition (K) factor at harvest than triploids in both treatments, while triploid K factor was significantly reduced by mixed rearing with diploids. Triploids had a significantly higher incidence of cataract than diploids in both treatments (60.9–77.3% vs. 21.7–47.2%, severity≥1). However, severity of cataract was greater in both triploids (2.43) and diploids (1.44) grown in isolation than those grown in a mixed ploidy population (triploid 2.17; diploid 1.09). Triploids had a significantly higher prevalence of visible deformity than diploids (18.1 vs. 7.2%), however, triploids grown in isolation had significantly higher prevalence than triploids under mixed rearing (30.4 vs. 5.8%). Collectively, the results provide clear evidence that triploids perform very differently when reared in the presence or absence of diploid conspecifics. Furthermore, observations of reduced deformity and cataract in the slower growing mixed populations support the hypothesis that such malformations are in part a function of higher growth rate. The results of this study also indicate that care should be taken when designing conventional common garden experiments to evaluate family performance between ploidy as interactions between ploidy may influence growth traits, although family effects appear to remain consistent.
•Triploid salmon growth is negatively affected by communal ploidy rearing at sea•Malformation in both ploidy appears to be a function of faster growth rate•Genotype influences prevalence of deformity
PDF
