Concerns have been raised over fish fraud after several instances of mis-selling were caught by regulators last year as the price of more sought-after species continues to rise.
Seven of 91 products tested in 2017 were reportedly found to have contained a cheaper alternative to the item on the menu, such as catfish, whiting and haddock all masquerading as cod.
The tests, overseen by local authorities and submitted to the Food Standards Agency, were predominantly from small businesses such as restaurants and retailers.
"No step of the supply chain is completely free [from risk], that's why it's very important to invest in control, traceability and other means to minimise this problem."
In a statement an FSA spokeswoman said: "These figures are from local authorities, who carry out targeted sampling as part a wide range of measures, which include physically checking products, labels, menus and invoices.
"Each authority has responsibility for implementing their own food sampling programme based on a range of factors, including the results of past inspections. As the sampling is targeted, the number of unsatisfactory samples is not necessarily representative of the wider food industry.
"Where issues are found, local authorities can consider appropriate action to protect customers and improve compliance, which may include a formal warning or taking enforcement action, such as prosecutions or cautions."