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Founder of Sea Shepherd and co-founder of Greenpeace, "Captain" Paul Watson (captain in what, I don't know) stated that

Farmed Salmon is Poison

70% of salmon produced worldwide is farmed, That contains artificial dyes.farm raised salmon is not pink, It’s actually grey. Fisheries are aware of this which is why they add artificial dyes in the salmon’s feed, to give it the pink color. One of many chemicals they use is Canthaxanthin, This has been linked to cause sight loss in humans,

Farmed salmon could well be the most toxic food ever produced. Yet is promoted as being "Healthy"

Poor grammar issues etc. aside, I thought I would try and look into this.

According to WebMD

Canthaxanthin is used to reduce sensitivity to sunlight (photosensitivity) experienced by people who have a rare genetic disease called erythropoietic protoporphyria (EPP). In these people, sunlight can cause skin reactions such as rash, itch, and eczema. Canthaxanthin is also used to reduce sun sensitivity caused by certain medications and other conditions, but there is no good scientific evidence to support these uses.

In the side effects tab, it does say

When taken by mouth: Canthaxanthin is LIKELY SAFE when taken by mouth in food amounts. However, it is LIKELY UNSAFE when taken by mouth in amounts needed for artificial tanning. Some people who have taken canthaxanthin for these purposes have experienced eye damage and vision loss.

Could Captain Paul Watson be skewing this information? Is using Canthaxanthin in Salmon farming highly toxic to humans and damaging to human eye health?

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    This class of chemicals (terpenoids and carotenoids) is almost everything that you eat, is completely safe at levels found in foods, and almost universally would be bad for you if you purified them and ate them with a spoon. Is the question if it's safe to eat foods with this chemical (it is), or if there's some unique property of fish farming that makes it unsafe (I don't know if anyone's bothered to study this specific application as it's something that's safe in general).
    – CJR
    Mar 16 at 13:50
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    The old adage is, "It's the dose that makes the poison." I found an EU document where they found a safe level of consumption of 15 milligrams of canthaxanthin per day. The tanning pills they used to sell that caused health issues had 30 milligrams, consumed daily. Salmon meet has 6-10 milligrams per kg. So you'd have to be eating kilos of salmon on a regular basis. Mar 16 at 15:03
  • 5
    If you put that in an answer @jeffronicus with a link to the EU document, I would accept it. Mar 16 at 15:54
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    "Farmed salmon could well be the most toxic food ever produced" could well be the most ridiculous exaggeration ever produced.
    – barbecue
    Mar 16 at 21:16
  • 5
    No no, farmed salmon is poisson
    – OrangeDog
    Mar 18 at 8:35

1 Answer 1

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The claim is correct for:

  • Canthaxanthin is used as a colorant in foodstuff, particularly so in farmed salmon, but also eggs and poultry
  • Canthaxanthin does also occur naturally, in some fish, in tiny trace amounts
  • Canthaxanthin is linked to eye disease, like the aptly named "Canthaxanthin retinopathy",
  • the negative effects occur at relatively higher doses, which are usually not reached when eating salmon occasionally, but frequent consumption will bring some consumers easily above the acceptable daily intake threshold

Thus the claim is going most probably into hyperbole for "most toxic food". The exact doses for the development of the retinopathy are not known.

It is concerning that the colorant is frequently overdosed in farmed fish for the resulting assumed human intake. 80 mg/kg in feedingstuff is allowed, but it is calculated that 'safety' would be achieved by limiting that to 25 mg/kg, but market demand ensures that 80mg is still applied to achieve the desired colour.

In Europe the stuff is regulated as follows:

Canthaxanthin has been authorised at Community level under EC number E 161g as a colouring matter in feedingstuffs under the conditions set out in Council Directive 70/524/EEC on additives in feedingstuffs:

Maximum content mg/kg complete feedingstuff: 80 mg/kg

Use permitted from the age of 6 months onwards

The mixture of canthaxanthin with astaxanthin is allowed provided that the total concentration of the mixture does not exceed 100 mg/kg in the complete feedingstuff.

It has also been found in bacteria (Saperstein and Starr, 1954), crustacea (Davies et al., 1970; Thommen and Wackernagel, 1964) and various species of fish including carp Cyprinus carpio (Katayama et al., 1971; 1973), golden mullet Mugil auratus, annular seabream Diplodus annularis, and trush wrasse Crenilabrus tinca (Czeczuga, 1973). Canthaxanthin is not encountered in wild Atlantic salmon but represents a minor carotenoid in wild Pacific salmon (Kitahara, 1983; 1984a,b; Matsuno et al., 1980). It was also reported in the wild trout Salmo trutta (Thommen and Gloor, 1965).

Today the concentration of carotenoids (mainly canthaxanthin and astaxanthin) exceeds 8 mg/kg of flesh and all producers try to reach a level that represents a value of 16 on the "Roche Color Card" (Torrissen, 2000). It must be noted that this scale is specific for measuring the pink colour due to astaxanthin and is not adapted to the orange hue obtained with canthaxanthin. Although a linear relationship has been established between the Color Card Score and the astaxanthin content in fish flesh, no such data is available for canthaxanthin.

The development over time of processing and storage operations, which can impact on canthaxanthin flesh concentration (see 3.4), has led to an increased quantity of pigments added to the diet to compensate for the degrading effects of processing.

In wild fish, carotenoid levels of up to 20-25 mg/kg have been reported in the flesh of trout (Storebakken and No, 1992), a value comparable to that reported for coho salmon by Schiedt et al. (1981). It must be noted that canthaxanthin, when present, is a very minor component

Canthaxanthin is the sole pigment of the carotenoid family registered for the use in both animal feeds and human foods. In the European Union, it is also the sole carotenoid pigment for which an Acceptable Daily Intake (ADI) has been established (0.03 mg canthaxanthin per kg body weight).

— European Commission, Health & Consumer Protection Directorate-General, Directorate C - Scientific Opinions, C2 - Management of scientific committees; scientific co-operation and networks "Opinion of the Scientific Committee on Animal Nutrition on the use of canthaxanthin in feedingstuffs for salmon and trout, laying hens, and other poultry", Adopted on 17 April 2002. pdf

In that paper they show an estimated human consumption of this carotenoid is indeed from eggs, poultry and highest from farmed fish:

13.7mg/kg fish muscle, 300g of that per human and per day, yielding 4.11 mg/day, or 0.069 Canthaxanthin Daily Intake (mg/kg bw) for a 60 kg person.

The retinopathy can resolve over time, if one stops consuming it, which was previously done on purpose as a prescribed medicine, or over the counter as a tanning pill. That is now no longer allowed in many countries, but while those pills were available, the following long-term follow-up identified retinopathy patients who took 30mg a day for 2 months up to three years:

Canthaxanthin retinopathy was first described in 1982 by Cortin et al., and occurs as golden particles in the paramacular region after ingestion of high doses of canthaxanthin.
[…]
A decrease in the quantity of golden particles after termination of canthaxanthin consumption was noted upon repeat photography over a 1½-year period, and for up to 6 years, but we have demonstrated for the first time that complete disappearance of the golden particles may take more than 20 years.

— Arno Hueber & André Rosentreter & Maria Severin: "Canthaxanthin Retinopathy: Long-Term Observations", Ophthalmic Res 2011;46:103–106 DOI: 10.1159/000323813

Freely accessible:

[…] canthaxanthin retinal crystal deposition is a very common finding in patients with prolonged use of the drug. Symptomatic visual loss is less common and correlates with total dosage and possibly patient age.

— Robert A. Beaulieu et al.: "Canthaxanthin Retinopathy with Visual Loss: A Case Report and Review", Case Reports in Ophthalmological Medicine, 2013. doi

For the generalised title of the question, "is it toxic to human health", again the dosage makes a poison:

At high doses, canthaxanthin has caused a serious, potentially fatal blood disorder called aplastic anemia. Canthaxanthin can also cause diarrhea, nausea, stomachcramps, dry and itchy skin, hives, orange or red body secretions, and other side effects.

WebMD: Canthaxanthin - Uses, Side Effects, and More

Relying mainly on this fatal outcome:

The drug's present means of distribution makes monitoring for toxic effects difficult. Thus, the frequency of adverse effects associated with canthax- anthin use, such as bone marrow suppression, is unknown. Even if there is only a small risk of these toxic effects, the use of the drug for cosmetic purposes does not justify this risk.

A 20-year-old white woman had a 4-month history of malaise, headaches, […]
She reported that about 4 months prior to being hospitalized she took a course of "tanning pills" containing canthaxanthin, which turned her deep orange. […] the dose was not known […]

15 days after admission, at which time the hematocrit was 0.08 and the platelet count was 11.0x109L, the patient was discharged to her home at her request for what was expected to be terminal care. She died 48 hours later.

— Renata Bluhm et al.: "Aplastic Anemia Associated With Canthaxanthin Ingested for 'Tanning' Purposes", JAMA, 1990; 264 (9): p1141–1142.

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    I think you may need a space between the two ones, because "11/2-year" strangely reads like 11 / 2 or 5.5 years to me which is not helped because this is immediately followed by a reference to 6 years.
    – Michael
    Mar 17 at 3:08
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    So the acceptable daily intake is 0.03mg per kg of body weight or around 2mg for an adult but a 300g piece of salmon contains 4mg which is already twice that amount? A single day is probably harmless but that would mean eating a salmon steak a day every day is unsafe because of Canthaxanthin.
    – quarague
    Mar 17 at 12:08
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    @quarague If you eat 300g of salmon every day, it will soon become safe again, because your body weight will quickly increase past 60 kg. Mar 17 at 15:54
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    @DmitryGrigoryev 300g of salmon is less than 650 kcals, way below starvation levels. There are plenty of dietary contexts where this would be a reasonable daily consumption of this particular food without weight gain.
    – Tiercelet
    Mar 18 at 16:40
  • @Tiercelet You won't be able to eat "just salmon", you'll suffer from protein toxicity with such a diet, regardless of canthaxanthin levels. Mar 20 at 19:54

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