Astaxanthin as a Colorant in Salmonoid Populations
Astaxanthin is widely used as an additive in commercial salmon grow-out feeds as a colorant. This blog recaps current industry practices, wild salmon diets and concludes with results from our recent Amplifeed™ Topcoat trial showing salmon fan scores exceeding 30 is possible and economically practical for hatchery raised fish using non toxic natural astaxanthin.
Current Industry Practice & Regulations
Astaxanthin has three different stereo-isomers, 3S 3’S, 3R, 3’R and 3R, 3’S. Current industry practice uses synthetic astaxanthin which has a fixed racemic ratio of 1:2:1 or yeast derived 3R, 3’R as a colorant. The “R” isomers of astaxanthin are toxic. Synthetic astaxanthin is not allowed to be included in human foods in either the EU or the US. To avoid mortality in animal feeds, use is limited to grow-out feeds and regulated by the US FDA and EU counterparts to 80-100 ppm. Salmon fan color scores of 27-28 can be achieved at harvest with 8.4 ppm of synthetic astaxanthin in the flesh.
The low bioavailability and toxicity of yeast derived and synthetic astaxanthin comes from the “R” forms of the compound. Unlike natural astaxanthin, the “R” isomers cannot embed into the cell and mitochondria plasma membrane and do not act as mitochondria targeted antioxidants (MTAs). The R forms loosely bind to the fatty tissues in the muscle mass. On harvest, the loose bonds can be broken by process water/ice water further reducing color during processing and shipment.
Wild Salmon Diets
Salmon are hatched upstream into environments rich in di-esterified 3S, 3’S astaxanthin largely coming from the decomposed flesh of their parents.
During allometric development virtually 100% of their astaxanthin intake is metabolized as a MTA. As astaxanthin does not accumulate, the flesh stays white during this phase.
After smoltification and upon entering the ocean, their diet shifts to krill and artic shrimp. These animals both produce d-esterified 3S, 3’S (“natural”) astaxanthin at concentrations between 120 and 1200 ppm.
During the 60-200 gram phase, a well fed smolt will intake significantly more astaxanthin than is used as an MTA, building up flesh color as a result.
As the fish grows, their natural diet changes from krill/arctic shrimp to larger feeds such as squid and herring. These feed fish do not produce natural astaxanthin de novo and have lower ppm rates vs. krill/arctic shrimp rich diets.
Color scores for wild salmon depend on diet as well as variants. Natural astaxanthin levels ranging from 12-38 ppm. The deepest color is typically found in Sockeye which is a relatively smaller fish, spending more time on krill/arctic shrimp diets vs. larger varieties such as King.
Color of 27-28 requires 34% less astaxanthin in the flesh vs. synthetic (5.5 ppm, I.A. Johnston et al. / Aquaculture 256 (2006) 323–336) due to higher bioavailability.
Sustainable Nutrition (SN) , together our sister hatchery, Sustainable Aquatics Inc is developing optimal dosing protocols of our Amplifeed ™ Topcoat micronutrient supplement with the goal of delivering high growth rates, >98% egg to harvest yields and deep color.
November 2020 Cohort
We hatched 1000 all female eggs in November 2020. We achieved 160 gram average weight in 262 calendar days/3380 degree days post hatch. Yields to that weight were over 99%. Color scores at 160 grams were in the low 20s.
At 60 grams, we shifted to a commercial salmon feed containing 40 ppm of synthetic astaxanthin. We continued to supplement with natural astaxanthin at 40 ppm from 60 to 600 grams. Flesh color improved to 27 at 600 grams.
We theorized that if we boosted the natural astaxanthin dosing rates from 40 ppm to 100 ppm, we could achieve 30+ color scores through higher dosing rates and time. In 10 days, we hit 30+.
Di-esterified 3S, 3’S astaxanthin forms strong bonds with the cell and mitochondria plasma membrane. Color expression is a function of astaxanthin density. Color stability is a function of the bond strength. Di-esterified 3S, 3’S astaxanthin does not bleed out into process water/ice so color remains unchanged throughout the supply chain.
We know can tune color to anywhere we want to using non toxic natural astaxanthin. For our next cohorts, we will be mimicking wild salmon diets, setting color earlier in the cycle (@160-300 grams) then cutting dosing rates to levels sufficient to maintain color and act as a strong MTA promoting growth rates and reducing mortalities/deformities until harvest.