The rosy hue of salmon and the burst of orange in shrimps are not simply genetically coded colors, instead the diverse coloration results from their carotenoids-rich diet.
In the wild, each species of salmon consumes different proportions of carotenoid-rich crustaceans. For example, sockeye salmon appears blood red given their life-long carotenoid-rich zooplankton diet. Coho salmon switch from zooplankton to less carotenoid-concentrated small fish as they mature, thus they appear more orange. Without natural carotenoids, salmon flesh looks grey or beige. Thus, feed with added dyes from synthetic sources are fed to farmed salmons to obtain approximate coloration.
What are Carotenoids?
Carotenoids, also known as tetraterpenoids or organic pigments, are hydrophobic molecules located within cell membranes. Contributing to the yellow, orange and red coloration in the skin, shell or exoskeleton of species, over 600 carotenoids have been identified in plants, non-photosynthetic bacteria, yeasts, molds and animals
Classification of Carotenoids
There are two ways to group and categorize carotenoids: by species ability to biosynthesize carotenoid or by structure.
Structurally, carotenoids can be classified into carotene and xanthophyll. Carotenes are oxygen-free hydrocarbons and include α carotene, β carotene, Ƴ carotene and lycopene. Xanthophylls, on the other hand, are oxygen-containing hydrocarbons and include astaxanthin, canthaxanthin, cryptoxanthin and zeaxanthin.
Among the different carotenoid pigments, astaxanthin and canthaxanthin are most commonly used for aquaculture feed.
Aquatic species can be divided into 3 groups based on their different carotenoid biosynthetic capacities:
Animals that can convert lutein, zeaxanthin or intermediates to astaxanthin, and can store astaxanthin from diet directly into their body. Representatives: goldfish, red carps
Animals that can convert β-carotene and zeaxanthin to astaxanthin. Representatives: crustaceans
Animals that cannot convert β-carotene, lutein or zeaxanthin to astaxanthin but can transfer pigments from diet to their body tissue pigment, as free form or esterified. Representatives: sea bream
Functions & Sources of Carotenoids
Aside from coloration, carotenoids serve as pro-vitamin A, antioxidants, immunoregulators and participate in a range of cellular activities that benefit both hosts and humans. For example:
Carotenoids provide protection against damage by light and oxygen during photosynthesis.
Male fish with more intense coloration can attract better mates during breeding.
Carotenoids can improve fertilization and result in a higher proportion of fertilized eggs.
Dietary carotenoids have shown preventative benefits against specific cancers and eye disorders. The list continues.
Carotenoids come from both natural and synthetic sources. List of common sources:
Why Are Carotenoids Significant?
It pays to be pink. The color of salmon fillets and shrimps is one of the key attributes to consumer appeal and directly impacts product pricing. Paler salmon and shrimp are often downgraded, which reduces farmer returns.
Carotenoid astaxanthin not only improves color, it is also a proven antioxidant and enhances major immunity parameters in farmed species.
In 2022, Nofima launched the “Knowledge Mapping Pigmentation” project with funding from Norwegian Seafood Research Fund (FHF) for a duration of 2 years to tackle the recent drop in pigment astaxanthin levels in salmon fillets despite increase in astaxanthin concentration in salmon feed during sea growth phase. The goal is to understand the extend and prevalence of poor pigmentation both in terms of geography and length of production.
“Trials have shown that stress and handling can negatively impact the level of astaxanthin, a carotenoid pigment that is responsible for pigmentation in salmon,” said Ytrestøyl. “EPA and DHA levels in feed also have an effect, but we don’t yet know the mechanism behind this. We need to conduct more research into an optimal diet that produces sufficient color in salmon that are reared in challenging conditions. We have also been looking into land-based production, how this impacts pigmentation and the metabolism of astaxanthin, as well as nutritional needs in different production systems.”
Dr. Maria Darias of the French National Research Institute for Sustainable Development (IRD) in Montpellier, France, says that skin color regulation has been shown to be more complex, with other regulatory factors such as cortisol, prolactin, somatolactin, agouti signaling protein, melatonin and thyroid hormones also playing a role. Darias agrees with Ytrestøyl that rearing conditions, including nutrition, water parameters, tank coloration, UV and surrounding luminosity, can impact both skin and fillet pigmentation. (source: GSA)
For Curious Minds
Heidi Kuehnle, founder and CEO of Kuehnle AgroSystems, has developed an innovative, patented means for producing natural astaxanthin leveraging proprietary dark fermentation technology:
The dark arts: a novel means of producing natural astaxanthin for aquafeeds by The Fish Site
Faux Flamingo Craze
An intense obsession with flamingos led Avril Fulani, a British entrepreneur, to feed her neighborhood swans astaxanthin-enriched aquafeeds. Within two weeks the birds had turned a deep pink. Ms Fulani has now launched her own range of flamingo feed, called “Fauxmingo plus”.
“We all know the story of the ugly duckling that grew up into a swan, but now they can grow up into a flamingo too,” she observes.
Here’s more on this story.
References
Global Seafood Alliance - The importance of carotenoids in aquafeeds
Global Seafood Alliance - It pays to be pink: Farmed shrimp production chain protects its price points with pigmentation
The Fish Site - Are salmon as pink as they used to be?
Wild Alaskan Company - Salmon Color Guide: Why Salmon Is Pink or Red
Turkish Journal of Fisheries and Aquatic Sciences - Significance of Pigmentation and Use in Aquaculture