They Opened a CAN of Salmon that Had Been Expired for 50 Years, and What They Discovered Surprised Scientists: “It’s a Sign that the Fish Comes from a Healthy Ecosystem”

Tin cans forgotten for decades reveal valuable clues about the health of marine ecosystems. A team of American researchers has studied more than 170 cans of salmon, some of them 50 years old, in order to draw unprecedented conclusions.

Scientists at the University of Washington recently analysed cans of canned salmon dating from 1979 to 2021. Among them was a can that had been out of date for half a century. Inside, the researchers discovered anisaquídes, marine parasites perfectly preserved by the canning process. This was not a sign of danger, but a very positive ecological clue. Far from indicating poor quality, the presence of these parasites was a sign of a healthy marine ecosystem.

Chelsea Wood, co-author of the study, insists: “The presence of anisaquídes is an indicator that the fish in your plate comes from a healthy marine environment”. These parasites follow a complex cycle: first ingested by krill, they then move on to fish such as salmon, before finishing their development in the intestines of marine mammals. Their survival and abundance are therefore closely linked to the stability of an entire food web.

By comparing boxes from different decades, the researchers observed a gradual increase in the number of anisaquídes present in the salmon. This phenomenon could reflect a stable ecosystem, or even one in the process of regeneration. But other explanations are being considered, including the impact of climate change or the growth of marine mammal populations in the North Pacific region.

Despite their scientific interest, these parasites can be a danger to human health. Under certain conditions, they can cause severe food poisoning. This duality poses a challenge: how can we reconcile their essential role in the biosphere with the risks they pose to our food supply? Many efforts are being made to limit these dangers. Fish eaten raw, canned or dried must be either cooked at 60°C for at least one minute, or frozen for five days before consumption. But in the case of canned fish, the problem is avoided from the outset: the thermal sterilisation process used during canning eliminates any risk, making them perfectly safe to eat.

The next step for the research team will be to study old preserves in greater depth in order to gain a better understanding of long-term ecological dynamics and the effect of climate change on marine fauna. It’s an ambitious project, launched from a simple tin of salmon forgotten in a cupboard.