BHT

Butylated hydroxytoluene (BHT) is a synthetic antioxidant that is mainly added to fish oil to prevent the fat from going rancid.

Fish oil is used as an ingredient in fish feed, and some BHT is therefore present in that fish feed. BHT is found in many food products such as sauces, chewing gum and food oils, but in seafood it is only found in farmed fish that has been given feed containing BHT. This is the synthetic antioxidant most commonly found in fillets from farmed salmon.

There is no evidence of exposure to BHT causing any harm to humans, but experiments on rats have shown that it can be carcinogenic if taken in large doses.