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They Opened 40-Year-Old Cans of Salmon, and What They Found Changed Marine Science

UNITED STATES
Monday, May 12, 2025, 00:10 (GMT + 9)

Parasitic Time Capsules: 40-Year-Old Canned Fish Reveal Disturbing Changes in Marine Ecosystems

An innovative study published in Ecology and Evolution: Volume 14, Issue 4 analyzes parasites preserved in Alaskan salmon cans since 1979, uncovering a significant increase in some species and opening new avenues for understanding threats to the ecosystem.

Natalie Mastick y Rachel Welicky 

A team from the University of Washington has demonstrated that canned fish, far from being mere culinary relics, constitute a valuable and surprising source of information for studying a crucial yet often elusive component of marine ecosystems: parasites. Their research, published in the journal Ecology and Evolution: Volume 14, Issue 4, titled "Opening a can of worms: archived canned fish fillets reveal 40 years of change in parasite burden for four Alaskan salmon species," led by Natalie Mastick and Rachel Welicky, reveals how something as ordinary as an old can of salmon can hold vital keys for the protection of Alaskan salmon, marine mammals, their intricate ecosystem, and the economy of the communities that depend on it.

The Growing Problem of Marine Parasites

Awareness of the complexity of our oceans has grown, understanding that, beyond the provision of healthy foods such as fish, mollusks, and cephalopods, they harbor a myriad of organisms, including tiny living beings that can pose a risk to human health and wildlife.

Concern about parasites such as anisakis is increasing, which has driven regulations to prevent poisoning in the industry and catering, as well as the dissemination of good practices to the public. While its presence is known in various fish and preventive measures (cooking at 60ºC for at least one minute or freezing for five days for raw, salted, or pickled consumption), the perception of a recent increase persists, when in reality its presence is historical.

Anisakis, belonging to the family Anisakidae, whose larvae are responsible for infections that can severely affect populations of fish, marine mammals, cetaceans, reptiles, and even birds. Fish act as vectors of infection for other animals, with potentially devastating effects on certain populations.

[Image caption: The distribution of canned salmon samples available for each salmon species in each decade.]

Scientific research on these tiny organisms is relatively recent and faces significant limitations in analyzing their behavior, evolution, and impact on the marine environment, with scarce historical data available. However, a change in the landscape of parasitic risk in species such as salmon is increasingly evident, requiring an assessment of the evolution of parasitism and its possible short- and medium-term consequences to implement effective actions.

Aged Cans: An Unexpected Window into the Parasitic Past

Faced with the scarcity of historical data, the Mastick team turned to an unusual but extraordinarily valuable source of information: old and expired canned fish.

"Parasitological assessments of salmon are inconsistent over time, and although parasite data are sometimes recorded when processing fillets for the market, these data are rarely retained beyond a few years," the researchers explain, highlighting concerns about the changing dynamics of parasitism in Alaskan salmon.

[Image caption a: A photo of a nematode (red circle) in a canned salmon fillet. The nematodes coil within the muscle and form pockets that are easily detected when dissecting with forceps. (b) A nematode recovered from canned salmon, cleared with lactophenol solution. Nematodes were highly degraded during the canning process, to the extent that even clearing the recovered specimen could not give us sufficient information to form an accurate genus-level identification.]

Anisakids frequently use salmonid fish as intermediate hosts before reaching their definitive hosts, which can be birds or mammals such as the sea lion, porpoise, sea otter, seals, or cetaceans, marine mammals protected in Alaska since the 1970s, whose population increase may also have contributed to a higher prevalence of parasites.

The economic, social, and cultural significance of salmon and the natural environment in Alaska makes any alteration in Anisakid populations a serious threat. The key to addressing this problem lay, paradoxically, in the salmon themselves, even if they were specimens sacrificed, processed, and canned decades ago.

[Image caption (c) An ethanol-preserved, uncleared anisakid nematode, was identified at the family level by the presence of a larval tooth (LT) and an excretory pore (EP) ventral to it, as described by Hurst (1984). (d) A preserved, uncleared anisakid. The cuticle is very cloudy, and internal organs are not visible.]

"Canned fish constitutes an open window to the past, providing information that would otherwise be lost, including crucial data on changes over time in the parasite burden of fish species important from a commercial, cultural, and ecological point of view."

In their novel approach, the scientists examined dozens of cans processed between 1979 and 2019, belonging to four species of Alaskan salmon: chum (Oncorhynchus keta), coho (Oncorhynchus kisutch), pink (Oncorhynchus gorbuscha), and sockeye (Oncorhynchus nerka). In their natural habitat, in a balanced ecosystem, wild salmon ingest parasitized crustaceans or are invaded by their larvae, but the Anisakids die during the canning process. However, their remains remain in the can, allowing their analysis by the researchers.

The results revealed a significant increase in the Anisakid burden in pink salmon and chum salmon during the 42-year study period, a pattern not observed in the other two species. This unprecedented finding suggests a previously undetected increase in Anisakid nematodes in some Alaskan salmon species in the last four decades, possibly linked to climate change and the increase in marine mammal populations in the region.

The data collected by examining these unusual time capsules now opens a new and fascinating avenue of research to determine the factors influencing this increase in parasites and assess the level of threat to the fauna and ecosystems of Alaska and other regions of the world. Furthermore, by resorting to banks of old canned goods, scientists can obtain valuable information without the constant need to sacrifice live animals to advance their research.

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