Pigments in Salmon Aquaculture: How to Grow a Salmon-colored Salmon
One of the most common criticisms of farmed salmon is that it is "artificially" colored, or as critics love to put it, "dyed." A typical anti-farming article states that farmed salmon "rely on a dye to color their flesh pink. Without that added pigment, their meat would be a pale gray." A photo caption in another widely quoted story in Mother Jones magazine shows "a worker [pouring] food pellets laced with a dye that will turn the salmon's flesh pink." A 2003 class-action lawsuit filed by a Seattle law firm alleges that "Unlike wild salmon, farm-raised fish rely on chemicals to turn their flesh pink." Few if any critics can resist mentioning "Swiss chemical giant Hoffman La Roche" (a major supplier of the pigment used in salmon farming) and its SalmoFan, a set of color swatches used by farmers and buyers to judge and specify the color of farmed salmon.
Most of these same critics gloss over, if they acknowledge at all, the fact that the pigment in question, astaxanthin, is the same one that wild salmon eat in nature, giving the wild fish their characteristic red-orange color. So why is there such a fuss over feeding it to farmed salmon?
Astaxanthin (3,3'-hydroxy-ß,ß-carotene-4,4'-dione) is a carotenoid pigment, one of a large group of organic molecules related to vitamins and widely found in plants. In addition to providing red, orange, and yellow colors to various plant parts and playing a role in photosynthesis, carotenoids are powerful antioxidants, and some (notably various forms of carotene) are essential precursors to vitamin A synthesis in animals.
Seafood lovers may not be familiar with the word astaxanthin, but instantly recognize its effect in the color of salmon flesh, as well as the orange shell color of cooked shrimp, crab, and lobsters. (The color of astaxanthin-containing tissues depends on how the pigment is bound to proteins; raw lobster shells appear blue, and Dungeness crab shells purplish brown, but cooking frees the astaxanthin, turning the shells bright orange.) None of these larger marine organisms actually produces astaxanthin; in the ocean that role falls to microscopic algae, the base of the marine food chain. Astaxanthin from algae (along with smaller amounts of other carotenoids including canthaxanthin, lutein, and ß-carotene) is passed up the food chain via zooplankton to small fish and crustaceans, including the small shrimplike krill that are an important part of the diet of wild salmon. Lots of fish and marine mammals eat krill and plankton-feeding fish; but the salmonids (salmons, trouts, and chars) are unique in depositing dietary xanthins in their muscles in a form that dramatically affects the meat color.
Farmed salmon feed, which is largely based on fish meal, does not normally contain any crustaceans or other natural sources of xanthins, so the only way to grow a salmon-colored salmon (or "red-meat" rainbow trout or Arctic char) is by providing pigments in the feed. It is possible to incorporate pigment in the form of shrimp, krill, or crayfish byproducts, but the cost is very high and much of the accompanying meal is indigestible by the fish. A far more efficient way is to use isolated pigment, of either natural or synthetic origin.
Many of the naturally occurring carotenoids are easily synthesized, and some have been produced on an industrial scale for decades. A lot of early salmon feed formulas relied on synthetic canthaxanthin, a carotenoid commonly used as a food additive in products ranging from poultry feed to ketchup. But canthaxanthin turned out to be less effective and less stable in fish than farmers wanted. Astaxanthin provided better results, and has largely replaced canthaxanthin in most salmon farming nations. US salmon farmers were limited to canthaxanthin until 1995, when the FDA approved the use of astaxanthin in domestic salmon farming, and astaxanthin quickly became the pigment of choice here as well.
Synthetic vs."Natural" Astaxanthin
Manufacturers of synthetic astaxanthin claim that their product is "identical to astaxanthin in nature," but this claim is debatable. Like many organic compounds, astaxanthin occurs in several isomers, sharing the same molecular formula but differing in the geometric arrangement of atoms (including mirror-image "right" and "left-hand" forms and an intermediate symmetrical isomer). In addition, astaxanthin molecules may be "free" or "esterized" (the latter bound to one or two fatty acids). Natural sources tend to contain a mixture of isomers in free, monoester, and diester form, while synthetic astaxanthin consists entirely of free molecules.
How important is the difference? The data are not conclusive. Apparently, fish can process various forms of astaxanthin, often converting them in their own tissues. Krill contain mainly the esterized "right-hand" isomer, yet wild salmon (for which krill is an important food source) show mainly the free "left" isomer in their meat. Some studies have shown better color deposition results from this or that source of astaxanthin, while others found no difference.
Not all commercially produced astaxanthin is synthetic. At least two organisms, the yeast Phaffia rhodozyma (classified by some as Xanthophyllomyces dendrorhous) and the microalga Haematococcus pluvialis, can be cultured on a large scale and processed into a meal high in astaxanthin, and both support commercial enterprises selling "natural" astaxanthin for a variety of uses. Both yeast- and algae-based meals are approved for aquaculture feed by the FDA, but neither is permitted in Europe as yet. However, at least one Chilean salmon producer is using "natural" astaxanthin derived from Phaffia to support its claim to "organic" status for its salmon in the US market. (Whether farmed fish, or any fish for that matter, can appropriately be called organic is a topic for another article.)
Can Salmon Pigments Cause Retinal Damage?
Several anti-farming articles and sites have suggested a link between canthaxanthin and potential human eye damage. If ingested in sufficient quantity, canthaxanthin can form crystalline deposits on the retina. In the 1990s, driven largely by the use of relatively large oral doses of canthaxanthin in "tanning pills" (taken to give skin a suntanned color without the dangers of sun exposure), the Sceintfic Committee of Food of the European Union set standards for human canthaxanthin intake. While noting that the effects of canthaxanthin on eyesight were minor, reversible, and "not associated clinically with any significant adverse functional visual defects," the committee established a maximum allowable daily intake (ADI) of 0.03 milligrams of canthaxanthin per kilogram of body weight, which works out to 1.5 to 2.7 mg of canthaxanthin per day for the normal range of adult body sizes. Based on this standard, the committee in January 2003 reduced the maximum allowable portion of canthaxanthin in salmonid feed from 80 ppm to 25 ppm (no such action levels exist for astaxanthin).
Even strongly pigmented farmed salmon contain no more than 5 parts per million of pigment, so a 110-pound person would have to eat 10 ounces of salmon per day, and a 175-pounder more than a pound, to reach the ADI. And that's only if the salmon were colored exclusively with canthaxanthin, which few are these days.
All in all, the retinal damage "issue" is not an issue.
The Color of Deception?
Although the use of pigmented feed in salmon farming has never been a secret, the industry has not exactly gone out of its way to publicize the fact. It apparently comes as a huge surprise to farmed salmon opponents, who continually use it as an example of how the public is being "deceived." Both astaxanthin and canthaxanthin are permitted under US FDA regulations (21CFR73) as "color additives not subject to certification," a category that includes other coloring agents such as caramel coloring, annatto extract, and beet powder (as opposed to "certified" colors such as "FD&C Red No. 40"). FDA regulations include various rules on the use of these pigments, including the maximum amount that can be added to foods.
Where farmers and sellers have run afoul of federal law is in the labeling of farmed salmon. Under 21CFR73, salmonids fed with astaxanthin or canthaxanthin are considered to contain added color, which must be labeled as such "on the food or on its container or wrapper, or on any two or all three of these, as may be necessary to render such statement likely to be read by the ordinary person under customary conditions of purchase and use of such food." Another section of the regulations gives various labeling options, including "artificial color added'' (or simply "color added''), "colored with ______" or "_____ color" in the ingredients, or "an equally informative term that makes clear that a color additive has been used in the food."
Although these regulations have been on the books for years, they were rarely if ever enforced, at least at the retail level. However, in April 2003 the Seattle law firm Smith & Lowney filed a class action suit against three major grocery chains, claiming they had misled the public by concealing the presence of artificial coloring in the farmed salmon they sell. By early May, all three chains (Safeway, Kroger, and Albertson's) had begun posting signs on their fish cases and adding "color added" language on individual package labels in compliance with the rules. Smith & Lowney persisted with the suit for damages, but a Seattle judge dismissed it in October, ruling that enforcement of the applicable food laws was up to government and not individuals.
A Little More Red, Please
While it constitutes a tiny portion of salmon feed (50 to 100 parts per million), astaxanthin represents a major share of the cost, up to 20 percent. The reason farmers go to the expense is simple: the public expects salmon to look like salmon, and according to studies by the leading manufacturer of synthetic astaxanthin and canthaxanthin, will pay more for farmed salmonids with stronger color. With such an expensive ingredient playing such an important role in the value of the product, farmers, feed manufacturers, and salmon buyers have a shared interest in an objective standard for farmed salmon color. Pigment manufacturers supply just such a standard in the form of color samples; Roche originally produced a card with color squares along the edges, and recently replaced the card with a fan of swatches, the SalmoFan™. Rather than argue about whether this batch of salmon is paler than the last or try to describe just what shade of orange is ideal, buyers and sellers can simply specify "fillet color 29" or numbers for the acceptable range of colors.
Again, farmed salmon opponents seem to find the use of the SalmoFan appalling, citing it as additional evidence of a sinister plot to fool the public. Never mind the fact that color charts are an accepted market tool in many food industries, including wild salmon; buyers and sellers of wild salmon can refer to full-color charts published by the Alaska Seafood Marketing Association to grade all five commercial species of Alaska salmon. Admittedly, the situations are not the same; color grading of wild salmon simply acknowledges the natural variability of the wild product, as well as the correlation between color and quality.
Why are salmon farming opponents so fixated on the SalmoFan? Perhaps because it symbolizes the fact that farmed salmon is entirely a domesticated animal, raised in a controlled environment and dependent on human intervention for all its needs. The fact that farmers can determine the color of their fish by adjusting the amount of pigment in the feed, and can use color swatches as a tool to monitor the results and make future adjustments, somehow adds to the offensiveness of the whole process.
I don't get it. But I suspect it's part of a larger strategy to demonize salmon farming by association with all sorts of evil images of "synthetic" ingredients (some prefer the even more loaded but scientifically meaningless term "chemicals") cooked up in industrial facilities by big bad multinational corporations. There are plenty of grounds on which to question salmon farming and they will be dealt with in other installments of The Salmon Files but the use of pigmented feed is not a very compelling one.
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