1. Farmed Salmon
Farmed salmon are often fed an unnatural diet of grains, as well as antibiotics and other drugs, which can cause their flesh to turn a greyish color. To turn them the pink-red hue of wild salmon, the fish are fed synthetic astaxanthin made from petrochemicals, which is not approved for human consumption in some parts of the world. Farmed salmon fed these chemicals are banned in Australia and New Zealand.