Does selection for growth affect heart morphology in Atlantic Salmon? Evidence from image-based phenotyping

Summary

Mortality in farmed salmon can exceed 20% during the seawater grow-out phase, and a substantial proportion of mortality can be attributed to infectious and non-infectious heart diseases. Concerns have arisen that long-term selection for rapid growth may have led to maladaptive heart morphology relative to wild conspecifics, increasing susceptibility to stress and disease. Compared with other livestock, Atlantic salmon are relatively recently domesticated (~55 years), and examples of poor heart health from selection for growth have been documented in other domesticated species such as ascites in broiler chickens. However, commonly used measures such as heart weight cannot capture the complexity of heart structure, limiting our ability to evaluate genetically correlated responses to selection for growth. Our objective was to provide the first genetic assessment of complex heart morphology in Atlantic salmon and its genetic relationship to growth-related traits. Here we used computer vision to quantify phenotypic and genetic variation of heart morphology traits and their genetic correlations with growth. Hearts from 30 genotyped families in AquaGen's breeding nucleus in freshwater (FW;n = 751) and saltwater (FW; n = 839) were imaged following fixation in formaldehyde. Images were captured from ventrodorsal and lateral views, and six morphological metrics were derived: ventricular height-to-width ratio (VHW), bulbus-to-ventricle width ratio (BVW), bulbus arteriosus alignment angle (ABA), ventricle incline (VI), ventrical tip curvature (VTC), and bulbus offset distance (BOD). Average daily gain (ADG) was used as the primary growth metric. Heritabilities and genetic correlations were estimated using animal models with a genomic relationship matrix using ASReml-R. Most heart morphology traits exhibited moderate to high heritabilities in both freshwater and saltwater environments. Genetic correlations between heart traits and average daily gain were moderate in SW for BVW (0.35), VI (-0.29), and VTC (-0.47) and consistent in direction across environments. These results suggest that sustained selection for growth could lead to correlated changes in cardiac morphology, including a relatively larger bulbus arteriosus width (BVW) and a flatter and more rounded ventricular orientation in the lateral plane (VI). Our findings suggest that correlated changes in heart morphology could have occurred alongside continued selection for growth; however, whether these changes are maladaptive, neutral, or beneficial to health and welfare should be further investigated.

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DOI : www.iastatedigitalpress.com/wc...
NVA : hdl.handle.net/11250/5569122