Effect of elevated temperature on astaxanthin deposition and distribution in the fillet of Atlantic salmon (Salmo salar L.) post-smolt

Globally rising seawater temperatures require more knowledge on the effects of elevated temperature on the biology and product quality of marine aquaculture species. Tasmania is a climate change hot spot where sea temperatures commonly exceed 20°C for prolonged periods during summer. This is associated with decreased pigment-carotenoid concentrations and heterogeneous pigment-carotenoid distribution in fillet of harvest size salmon, leading to substantial product downgrade. The current research tested the effects of three factors: temperature (elevated; ET, 19.5°C and control; CT, 15°C), dietary oil blend (fish oil blend and canola oil blend) and fillet cut (anterior/dorsal cut; ADCT and dorsal Norwegian quality cut; dNQC) on the concentration of astaxanthin (Ax) in white muscle of post-smolt salmon after fish doubled initial weights. The concentration of Ax in white muscle was higher at ET and higher in the dNQC at ET, whereas the Ax concentration between the fillet cuts at CT was similar. Diet had a strong impact on the fatty acid composition in white muscle but did not affect Ax concentration. None of the factors affected the concentration of the oxidative stress-indices malondialdehyde in white muscle. No idoxanthin was present in any of the white muscle samples, indicating that no metabolic conversion of Ax occurred in this tissue. When Ax was expressed per unit of crude protein, the concentration of Ax in crude protein was higher in the dNQC at ET. Our research provided the first experimental evidence of the importance of temperature on carotenoid deposition and distribution in the fillet of Atlantic salmon. Ax concentration was not affected by dietary oil blend and was not associated to oxidative stress or its metabolic conversion in muscle. Differences in the concentration of Ax per unit of crude protein between the fillet cuts at elevated temperature could be the first evidence for differences in the Ax binding capacity of myofibrillar white muscle proteins in different fillet areas. Elevated temperature did not limit the deposition of Ax. However, heterogeneous pigment-carotenoid distribution in the fillet is undesirable for marketing.