Carotenoid and lipid content in muscle of Atlantic salmon, Salmo salar, transferred to seawater as 0+ or 1+ smolts

Abstract

Accumulation of lipids and carotenoids, including 4′-hydroxyechinenone (4′-hydroxy-β,β-carotene-4-one), growth and condition factor were investigated in Atlantic salmon ( Salmo salar) transferred to seawater as 0+ and 1+ smolts. Salmon were fed a diet with 30 mg/kg astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) and 30 mg/kg canthaxanthin (β,β-carotene-4,4′-dione) for 35 weeks. The 0+ smolt contained more carotenoids than the 1+ smolt when mass differences were corrected for ( P<0.0001), a difference also reflected by the tristimulus colour measurements (C1E a*- and b*-values). Astaxanthin and canthaxanthin comprised more than 93% of the total carotenoids, but small differences were observed in carotenoid composition. The condition factor was significantly higher in 0+ than 1+ smolts after correction for mass differences ( P<0.01). There was a high correlation between ln-transformed muscle lipid (%) and ln-transformed body mass for 0+( R 2=0.94) and 1+smolts ( R 2=0.97). The canthaxanthin metabolite 4′-hydroxyechinenone was isolated from muscle of Atlantic salmon fed a diet supplemented with canthaxanthin. It was characterised and identified by its absorption maximum ( λ max=458 nm in n-hexane), mass spectrometry ( M +=566) and co-chromatography with authentic standard obtained by NaBH 4-reduction of canthaxanthin on thin-layer chromatography and HPLC. HPLC of the camphanates of 4′-hydroxyechinenone revealed a stereoselective transformation in favour of the (4′ S)-isomer, the (4′ S) and (4′ R)-isomers comprising approximately 81 and 19% of the total 4′-hydroxyechinenone, respectively. The percentage of 4′-hydroxyechineone of total carotenoids ranged from 1.3 to 3.1% and declined with fish size ( P<0.001). We conclude that effects of time of seawater transfer of Atlantic salmon smolts have significant effect on carotenoid accumulation and other quality traits. The detailed biochemical and physiological basis for these differences require further elucidation.