Uptake in the fillet and metabolism of pigments in rainbow trout onchorynchus mykiss fed diets containing synthetic astaxanthin or red pigments of microalgal and bacteri

Carotenoid pigments such as astaxanthin and canthaxanthin are responsible for the characteristic pinkred coloration of salmonid flesh, with additional pigments like adonirubin, 3-hydroxyechinenone, adonixanthin, asteroidenone, and echinenone playing roles as metabolic intermediates or minor
contributors. These pigments are not synthesised de novo by salmonids but are absorbed from the diet, metabolised in the liver, and deposited in muscle tissue. Synthetic astaxanthin is commonly used in
industry, with organic alternatives of microalgal and bacterial origin occupying a limited place in this space
with no available documentation on their pigmentation efficiency in trout. Triplicate groups of rainbow trout
(Onchorynchus mykiss) were reared from 25 g to 125 g body weight during 8 weeks in tanks, fed one of
four diets, containing no (control), or approx. 30 ppm astaxanthin (free and astaxanthin esters), synthetic– CAROPHYLL
®Pink–SA, from dried Haematococcus pluvialis–AA, or the bacterial biomass Panaferd
©–PA). CAROPHYLL
®Pink contained nearly only free astaxanthin (approx. 100,000 ppm), Haematococcus
pluvialis biomass contained mainly astaxanthin esters (97%) and less free astaxanthin (3% of 6,900 ppm
total astaxanthin), while Panaferd
© of approx. 36,000 ppm total astaxanthin contained 67% free
astaxanthin, 33% astaxanthin esters, it contained 9,640 ppm adonirubin, and lower amounts of
canthaxanthin (2,010 ppm). No treatment differences were observed on growth, biometrics, or feed
efficiency. The sum of fillet pigments was double as high in SA and PA (total carotenoid apparent
digestibility coefficient –ADC– 77 and 75%, respectively) as compared to AA (48% total carotenoid ADC).
Irrespective of pigment source, it was mostly free astaxanthin detected in the fillets. Much lower amounts
of canthaxanthin and adonirubin were identified in fillets of fish in the AA and PA treatments, in addition to
low levels of 3-hydroxyechinenon, adonixanthin, asteroidenon and echinenone detected in PA. The main
pigment analysed in the liver was again free astaxanthin, but significant amounts of adonirubin were also
found both in AA and PA, and smaller amounts of canthaxanthin were SA, AA and PA. Significant
amounts of pigment metabolites (94ppm β-caroten and 92ppm 3-hydroksyechinenon) were found in fish
faeces in AA, and PA (89ppm adonixanthin), unlike SA and control treatments.