University researchers investigating food fraud revealed something fishy about a quarter of the cod and haddock sold in Dublin - it's another species.
Genetic checks by a team from UCD even discovered some exotic sounding but foul tasting varieties being used as substitutes for the much-loved whitefish.
Lead researcher Dr Stefano Mariani said the level of fraud for smoked cod and haddock was 82%.
"The high levels of cod mislabelling found in Ireland gives a false perception of market availability, allowing consumers to believe that because cod is so widely available, the stocks must be healthy," Dr Mariani said.
The study, which used DNA barcode tests on fish from 80 supermarkets, fish and chip shops and fishmongers across north and south Dublin, found the traditional chipper was the worst offender.
Dr Mariani suggested fish and chip shop owners may not be to blame because of the amount of smoked fish they buy in.
The study revealed mainly pollock, coley and whiting were being used instead of cod and haddock but it also discovered a non-native species - the unpleasant greater argentine.
Cod stocks around Ireland and Britain have been at critical levels for years with the Irish Sea and North Sea virtually depleted.
But Dr Mariani, from UCD`s School of Biology and Environmental Science, said the use of coley and pollock could open new markets and allow depleted stocks to recover.
The team intend to develop the research, published in the Ecological Society of America, and hopefully discover who is at fault for mislabelling fish products.