Heterogeneous astaxanthin distribution in the fillet of Atlantic salmon post-smolt at elevated temperature is not affected by dietary fatty acid composition, metabolic conversion of astaxanthin to idoxanthin, or oxidative stress

Abstract

Farmed Atlantic salmon in Tasmania are exposed to elevated water temperatures during summer, which is often associated with reduced pigmentation quality. This study tested the effects of the factors: temperature (elevated, 19.4 °C (ET) vs. control, 15.2 °C), dietary fatty acid (FA) composition (diet 1, high in fish oil vs. diet 2, low in fish oil) and fillet cut (anterior/dorsal cut; ADCT and dorsal Norwegian quality cut (dNQC)) on the concentration of astaxanthin (Axn) in white muscle of salmon post-smolt. After fish doubled initial weights (212 g) at each temperature, the concentration of Axn in muscle was not affected by dietary FA composition, but was higher at ET and higher in the dorsal NQC at ET. In contrast, Axn concentrations between these fillet cuts were the same at the control temperature. The concentration of long chain polyunsaturated FA, which are prone to peroxidation, was generally higher in the fish fed the diet high in fish oil, and in the anterior/dorsal cut. However, the relationships between these FA within triglycerides and phospholipids and the lipid peroxidation product malondialdehyde in white muscle were poor. Further, the concentrations of malondialdehyde showed a poor relationship with Axn in white muscle. There was no idoxanthin in any of the white muscle samples at the analytical detection limit of 0.1 mg/kg.In summary, ET led to higher concentrations of Axn in white muscle, but also to heterogeneous Axn concentrations between the fillet cuts tested. The concentration of Axn in white muscle was not affected by the dietary FA composition and was not associated with oxidative stress or metabolic conversion into idoxanthin in this tissue under the conditions tested. When Axn was expressed per unit of crude protein, the concentration of Axn was higher in the dorsal NQC at ET, indicating that differences of myofibrillar white muscle proteins in their capacity to bind pigment carotenoids may have contributed to the heterogeneous pigment deposition in fillet at ET.Global sea temperatures are anticipated to rise in the future and the implications for aquaculture production must be understood. This study demonstrated the significant effects of temperature on the deposition of pigment carotenoids over the fillet of salmon.