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A multidisciplinary team of researchers, including archaeologists, have analyzed the DNA of fish remains from Roman fish fermentation vats, creating a method to identify animal remains when they are damaged beyond recognition.

Fish were a vital source of protein for the Romans and they were often preserved through salting and fermenting, producing fish pastes and sauces. The most famous of these was garum—a sauce popular as an umami-flavored seasoning and condiment.

Garum was both prepared for local consumption and to be traded long distances, with its long shelf life facilitating commerce across the empire. As such, large-scale fish-salting plants known as cetariae were constructed in coastal areas, particularly on the Atlantic coasts of Hispania (modern Iberia) and Tingitana (modern Morocco), which were famous for their fish sauces.

Because fish remains are so fragile, they are often found damaged beyond recognition, not identifiable via observation alone. This is especially true for those from salting vats, since they were intentionally crushed during sauce production.

Analyzing their DNA to empirically determine their species provides a potential solution, but even this is not perfect. In the case of fish pastes and sauces, the grinding and fermentation processes accelerate DNA degradation.

"Fish bones are a frequent find in the archaeological record of the Roman period, yet their use in archaeogenomic studies is residual, probably due to the fragmentary nature of remains, which makes identification to species or even genus difficult," states corresponding author, Dr. Paula F. Campos from CIIMAR, Universidade do Porto.

To determine whether ancient DNA studies could be performed on these highly-processed remains, researchers extracted and sequenced the DNA of fish remains from a fish-salting vat at the cetaria of Adro Vello, north-west Spain. This key archaeological site is the focus of a multidisciplinary project led by the Archaeology Department of the University of Vigo. Their results are published in the journal Antiquity.

By comparing the DNA sequences from the archaeological remains with those of modern sardines, the researchers determined that Roman-era sardines were closely related to those found in the same area nowadays, confirming genetic continuity despite the high mobility of the species.

Overall, these findings confirm the value of ancient DNA studies for identifying animal remains that have been damaged.

This has significant implications for the study of archaeological fish remains in the future.

"In this study, we demonstrate that usable DNA can survive in fermentation environments, such as the brines used by the Romans to make garum," concludes Dr. Campos. "Despite enduring conditions that promote the degradation of DNA, the methods we outline allow for the identification of species from these processed bones."