A New Chemical Method for Distinguishing Between Farmed and Wild Salmon

Wild salmon and farmed salmon can now be distinguished from each other by a technique that examines the chemistry of their scales.

Dr Clive Trueman, who is based at the National Oceanography Centre, Southampton, said: “Salmon farming is a big, intensive business. In 2006, around 130,000 tonnes of salmon were farmed in Scotland for the table. Wild populations of Atlantic salmon are in serious decline across their whole range and the total wild population returning to Scottish rivers in the same year is estimated at less than 5000 tonnes. Wild fish are rare and expensive so there is a strong incentive for fraudulent labelling. Farmed fish also escape into rivers, harming the wild population. Unfortunately, it can be difficult to distinguish between farmed and wild fish.”

This new work, done in collaboration with the Scottish Association for Marine Science (SAMS), Oban, will help to crack this problem.

Fish scales are formed from the same chemicals as bones and teeth and grow like tree rings, preserving a chemical record of the water the fish lived in throughout its whole life. Scales are easy to collect, and can be removed from fish without harming them – which is important when studying an endangered population. The team discovered that levels of the trace metal manganese were always much higher in fish of farmed origin.