The effect of triploidy on the culture performance, deformity prevalence, and heart morphology in Atlantic salmon

The study objective was to compare the effect of ploidy on growth, downgrading, discards, and fish quality at slaughter, the prevalence of skeletal deformities (external examination: spinal, jaw and operculum; radiology: spinal), and heart morphology from a large production of diploid and triploid Atlantic salmon (Salmo salar) reared in triplicate (n=20000ploidy−1). Triploids were 15% heavier and 7% longer than diploids at seawater transfer but diploids were 10% heavier and 1% longer than triploids at slaughter. Triploidy had no effect on gutted mass for each quality classification but significantly reduced the percentage of fish classified as superior whilst increasing the amount of production and discard quality (mean %±SE (n=3ploidy−1): superior, 89.6±1.8 vs 83.7±1.4; production, 2.4±0.5 vs 6.5±0.1; discards, 0.9±0.2 vs 2.1±0.2 for diploids and triploids, respectively). As a result, less money was received per triploid fish compared to diploids (the average price fish−1 cage−1 (n=3 ploidy−1) ranged between 62.3–81.1 and 63.5–67.4 Norwegian kroner for diploids and triploids, respectively). Total discards and downgrading were increased by triploidy due to deformities and triploids also had more fish discarded due to “small fish” compared to diploids. Radiography demonstrated triploids had more fish with one or more deformed vertebrae (mean %, 22.0 vs 42.7 and 24.4 vs 48.9 in diploid and triploid, parr and post-smolts, respectively). Diploid seawater mortality was significantly lower than triploids (1.2–1.5 and 1.8–2.2% cage-1, respectively). Triploid food conversion ratios (FCR) and specific growth rates (SGR) were inferior to diploids during the latter half of seawater phase (range: FCR, 1.36–1.47 and 1.55–1.67; SGR, 0.49–0.53 and 0.44–0.46 for diploids and triploids, respectively). Triploids had a lower angle of the bulbus arteriosus at slaughter (mean angle±SE (n=3 ploidy−1): 46.5±0.1 and 39.1±1.3 in diploids and triploids, respectively). There was no effect of triploidy on ventricle mass, ventricle roundness, or the compact:spongy myocardium ratio. Sex had a significant effect on body length and ventricle mass with males 3% longer and having hearts 5.8% heavier than females. Overall the present data would suggest triploids are suitable for culture purposes but at a higher economic cost to the producer. In addition, future work should focus on reducing the prevalence of deformities in order to improve triploid quality and welfare.