Expired cans of salmon reveal a big surprise

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Canned salmon are the unlikely heroes of an accidental back-of-the-pantry natural history museum, with decades of Alaskan marine ecology preserved in brine and tin.
Parasites can tell us a lot about an ecosystem, because they’re usually up in the business of several species.
While the idea of worms in your canned fish is a bit stomach-turning, these roughly 0.4-inch (1-centimeter) long marine parasites, anisakids, are harmless to humans when killed during the canning process.
“Everyone assumes that worms in your salmon is a sign that things have gone awry,” says Wood.
This is how they end up in the salmon, and eventually, the intestines of marine mammals, where the worms complete their life cycle by reproducing.
They found worms had increased over time in chum and pink salmon, but not in sockeye or coho.
“Seeing their numbers rise over time, as we did with pink and chum salmon, indicates that these parasites were able to find all the right hosts and reproduce.
Mastick and colleagues think this novel approach – dusty old cans turned ecological archive – could fuel many more scientific discoveries.


With decades of Alaskan marine ecology preserved in brine and tin, canned salmon are the improbable heroes of an unintentional back-of-the-pantry natural history museum.

Because they typically intertwine with multiple species, parasites can reveal a great deal about an ecosystem. However, historically, we haven’t given them much thought unless they pose a serious threat to humans.

For parasite ecologists like Chelsea Wood and Natalie Mastick of the University of Washington, who have been trying to figure out how to track the effects of parasites on marine mammals in the Pacific Northwest in the past, this presents a challenge.

In response, Wood said categorically that she would be happy to take boxes of dated, dusty salmon cans—dating back to the 1970s—off of Seattle’s Seafood Products Association when they called.

The ecologists handled the cans, which had been stored for many years as part of the association’s quality control procedure. What they found inside was an archive of remarkably well-preserved specimens—not of salmon, but of worms.

Although the thought of having worms in your canned fish may make you gag, anisakids, which are marine parasites about 0.4 inches (1 centimeter) long, are safe for humans to consume once they are killed during the canning process.

“Most people believe that the presence of worms in their salmon indicates a problem,” mentions Wood.

However, many elements of the food web are integrated into the anisakid life cycle. They are indicators of a healthy ecosystem, in my opinion, that the fish on your plate came from. “.

After krill eat anisakids, larger species eventually consume them, allowing anisakids to enter the food chain. By reproducing, the worms finish their life cycle in the intestines of marine mammals, which is how they end up in salmon. The cycle starts over when the mammal releases its eggs into the ocean.

The lead author of the study, Wood, states that anisakid populations will decline if a host—marine mammals, for example—is absent.

42 cans of chum (Oncorhynchus keta), 22 coho (Oncorhynchus kisutch), 62 pink (Oncorhynchus gorbuscha), and 52 sockeye (Oncorhynchus nerka) were among the 178 tin cans in the “archive” that included salmon from four different species that were caught in the Gulf of Alaska and Bristol Bay over a 42-year period (1979–2021).

The researchers dissected the filets and worked out how many worms there were per gram of salmon, despite the fact that the methods used to preserve the salmon, thankfully, do not keep the worms in perfect condition.

On chum and pink salmon, but not on sockeye or coho, they discovered that the number of worms had grown over time.

It is evident that these parasites were successful in finding suitable hosts and proliferating when their numbers increase over time, as we observed with pink and chum salmon. According to Mastick, the lead author of the paper, “that could indicate a stable or recovering ecosystem, with enough of the right hosts for anisakids.”.

It is more difficult to account for the steady worm counts in coho and sockeye, though, given that the canning procedure obscured the anisakid species.

The authors state, “Although we are confident in our identification to the family level, we could not identify the [anisakids] we detected at the species level, so it is possible that parasites of a stable species tend to infect coho and sockeye, while parasites of an increasing species tend to infect pink and chum salmon.”. “.”.

Mastick and colleagues believe that a lot more scientific discoveries could come from this innovative method of turning old, dusty cans into an ecological archive. It appears that a lot of worms have been revealed.

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