Carotenoids in aquaculture

It is generally accepted that the colour of salmon products is one of the most important quality parameters.  Therefore, colour plays a decisive role when evaluating the quality of the product at point-of-sale.  The species-specific pink flesh colour provided only by astaxanthin has always been associated with salmonids and has differentiated the salmonids from other fish species.  Studies have shown that when it comes to making purchasing decisions about salmon, consumers have stated that colour is very important.

Carotenoids are used in aquaculture feeds to provide the colour associated with consumer products, such as the bright vibrant colours of ornamental fish.  The same carotenoid, astaxanthin, found in wild salmon is used in aquafeeds to impart this natural, pink-red colour to farmed salmon fillets.  Colour matters, particularly in regards to consumer preference for aquaculture products.

As is the case with other carotenoids, salmonids cannot endogenously synthesise astaxanthin; therefore, it must be supplemented in the fish’s ration.  Research also indicates additional benefits from dietary carotenoids beyond the resulting colouration.  Astaxanthin, for example, has biological functions related to growth, reproduction and tissue health in salmonids and shrimp, possibly due to the compound’s strong antioxidant properties.

Only a small number of plants and micro-organisms can synthesise carotenoids.  Higher animals, including fish, cannot produce the carotenoids themselves and are reliant upon a dietary source.  They absorb the carotenoids from the feed and deposit them in their tissues.

Astaxanthin is the pigment that provides salmon flesh with its characteristic rich pink-red colour and the major carotenoid in the integument and internal organs of red sea bream.  Astaxanthin accounts for more than 90% of the total carotenoid content found in the flesh of wild salmonids (salmon and trout).  In the wild, fish absorb astaxanthin from the crustaceans they eat.  The absorbed carotenoid is then transported in the blood to the muscles and skin where it is deposited. 

In other fishes and to a limited extent in salmonids, additional carotenoid compounds are the source of other bright colours.  Research results indicate that tunaxanthin is a rather common pigment in marine fish.  This carotenoid is especially abundant in yellow-coloured fishes, like yellowtail (Seriola quinqueradiata).  Astaxanthin, by contrast, seems to be dominant in red marine fish.  Lutein is also widely found in many marine species.  Carotenoids commonly occurring in freshwater fish include beta-carotene, lutein, taraxanthin, astaxanthin, tunaxanthin, alpha-, beta-doradexanthins, and zeaxanthin.

Nature-identical astaxanthin versus natural astaxanthin

The main carotenoid used throughout the world in intensive aquaculture is astaxanthin.  There are a number of alternative sources of astaxanthin (krill, shrimp, crawfish, a basidiomycetes yeast, or algae), although the major source is CAROPHYLL® Pink.

The bulk of the astaxanthin available globally for salmonid pigmentation is manufactured by chemical synthesis.  The molecule is built from smaller molecules, which are linked using appropriate reactions.  Astaxanthin manufactured by synthesis results in a pure crystalline compound that is identical to the molecule produced by biological synthesis.  Nature-identical astaxanthin from CAROPHYLL® Pink is identical to astaxanthin in nature.

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Information provided by Roche S.A.