Much like in the 2013 horsemeat scandal, eating cheaper fish does not present a health risk, but concerns have been raised about consumer deception.
“It probably does go on,” said Andrew Cook, president of the National Federation of Fish Friers.
The Lancashire businessman, who runs a chip shop in Chorley, has been in the business for almost 30 years.
He said: “I was only talking to somebody the other day who went into a pub and ordered fish and chips and he thought it was pangasius and when he tackled them about it, they said it was.
“It is fine to eat, there’s nothing wrong with it, but when you go and get fish and chips most people expect a marine species, so cod, haddock or plaice.
“I think if you’ve got something that’s farmed, like pangasius, as long as it’s advertised as such that’s fine.
“It’s when it’s being sold at a cod price that’s a problem and shops need to be careful about doing that.”
Crook urged chip shops to list the species on their menus, adding: “As an industry, we’ve got to have the trust of the general public.”