I googled astaxanthin and found a website talking about how it's an antioxidant and prevents cancer and is necessary for the healthy growth of the farmed salmon.
Surely that can't be true.
Via the blog
That is technically true, but there is more to this story.
While both astaxanthin and canthaxanthin are deemed safe by the Food & Drug Administration (although people trust that organization to varying degrees), certain concentrations of canthaxanthin have been associated with eye defects.
Interestingly, different countries have different ideas of how many parts per million of that synthetic dye are "safe."
That being said, the vast majority of salmon farmed in the United States and Europe is only fed astaxanthin.
In other parts of the world, though, farmed salmon is only fed canthaxanthin (it is the cheaper of the two dyes.)
I still would not be too worried. You would need to be eating a LOT of salmon dyed with canthaxanthin to be affected.
What all of this ties into, though, is another controversial topic – COOL (Country of Origin Labeling.)
Although it is required for all fish sold in the United States, I have seen it very sparingly in supermarkets.
As far as I am concerned, the core issue surrounding these food dyes isn't so much possible health repercussions, but rather truthful advertising to consumers.
If farmed salmon were to either remain gray or be dyed another color (say, white), then consumers would immediately know they are not purchasing a wild variety, and there would be no room for mislabeling (remember this infamous study by Marian Burros of The New York Times?).
Since farmed salmon is nutritionally inferior to its wild counterpart (more saturated fat, higher Omega 6 fatty acid content, lower Omega 3 fatty acid content), people should not be left in the dark.
This is not to say farmed salmon should completed avoided or viewed in the same light as deep fried fish nuggets, but consumers have a right to know exactly what they are putting on their plates.