The 'Ask Italian' restaurant chain – part of the Azzuri Restaurants group – has been fined £40,000 by Swansea Magistrates after pleading guilty to an offence under the Food Safety Act 1990.
The offence related to the discovery by Swansea Council Trading Standards that the restaurant's most expensive dish - 'Aragosta e gaberoni' or Lobster and King Prawn, was found to contain only a small amount of lobster.
The council said the discovery was made during a routine inspection when a request to see the dish raised concerns that the meal did not resemble lobster.
Subsequent testing highlighted the fact only a third of the dish was made from lobster with the remaining elements containing white fish and filler.
Rhys Harries, Swansea Council's Trading Standards Team Leader, said: "Our role as trading standards is to ensure restaurants accurately describe the food on menus and that it reflects what appears at their table.
"When our officers visited the restaurant in March 2019, our investigations prompted some concerns over their most expensive dish which was described as lobster.
"We felt that the description on the menu compared to the product actually served was likely to mislead customers as to the substance of the food."
Mark Thomas, Swansea’s Cabinet Member for Environment and Infrastructure Management, said: "Customers who pay good money to eat at restaurants should actually be served with what they believe they have paid for. Our view is that customers were being misled and not aware of the additional ingredients in the meal.
"I'm pleased that our observant Trading Standards Team has been able to uncover this issue and hopefully it sends a strong message out to other restaurants, regardless of their size, that we will continue to check up on these issues to ensure customers in Swansea and elsewhere are being treated fairly.
"I'm also pleased the Magistrate has recognised the efforts of Swansea Council and our Trading Standards by commending the team."
ASK has been approached for comment.
The BBC said the company had apologised for what it described as an error, and accepted that without reference to white fish, the menu description was incomplete and likely to mislead.
The report added: “It denied having a financial motivation and said the item had the lowest profit margin of all the restaurant's pasta dishes, adding there was no health and safety risk associated with this case.”