'Sustainable' cod may be no such thing

Marine ecologists at LJMU are applying DNA technology to reveal the source of Britain’s favourite fish.

Dr Marine Cusa and Professor Stefano Mariani use genetic techniques to verify the species and geographical origin of the cod filets that end up on our plates.

In a recent study they found the origin of almost one in three cod incorrect when bought from a random mix of European fishmongers and supermarkets.

According to Professor Mariani, identifying genetically distinct populations is a key task to ensure stock sustainability, and the technology is now available to the authorities.

He said: “With these relatively inexpensive, diagnostic tools we can effectively monitor when the fish we buy is coming from a sustainable source”.

Cod quotas

Cod quotas vary hugely according to which part of the Atlantic is being fished. The Northeast Arctic cod stock is doing relatively well and has strong management measures with a declining quota in 2025. On the other hand, the North Sea and Baltic Sea stocks recently collapsed, leading to severe fishing restrictions.

Dr Cusa said: “Interestingly, the highest percentage of mislabelling was for Northeast Arctic cod mislabelled as North Sea cod.

“This might be due to deliberate mislabelling because consumers like to purchase local fish; the fish is labelled as a ‘North Sea’ product when in truth, it’s fished very far away in the high Arctic.

“This gives the false impression to consumers that local fish are still being harvested, possibly sustainably, and are present in the market, when in reality, their stock has collapsed.” The authors believe that this approach could be extended to dozens of widely distributed commercially exploited species.

The study, which also involved the University of Edinburgh, and reported in The Conversation, is published in Fisheries Research https://authors.elsevier.com/sd/article/S0165-7836(25)00039-6.