Fish bite back

booby trapped salmon

An Alaska pink salmon and the booby trap waiting inside/CDC

As Alaska heads into the season of the salmon, it is worth noting the story of a raw-fish eater who made the news at the end of last week for the tapeworm he was found to be carrying in his gut.


The 32-year-old “man from Lisbon, Portugal, is featured in the medical journal BMJ Case Report,” CBS News reported.  “The man was suffering from a bout of stomach pain for more than a week, and experienced vomiting and a fever.

“When doctors questioned him about his symptoms and history, he revealed that he had recently eaten sushi.”

Sushi, as the story notes, is generally considered very healthy. But in this case it was made with fish infected with parasites, a fairly common phenomenon .

What kind of parasite-laden fish the man ate was not mentioned in the story, although reporter Mary Brophy Marcus did note the danger of “raw or undercooked seafood such as cod, fluke, haddock and monk fish.”

Somehow she left out the species about which the Centers for Disease Control warned last February: salmon, particularly Alaska salmon.

The CDC cited the Japanese broad tapeworm as an “emerging infectious disease” in Alaska salmon.

“Recent studies that used molecular methods indicate that the number of human cases caused by this tapeworm may have been highly underestimated,” the CDC reported. “In addition, increasing popularity of eating raw fish is probably responsible for the increased number of imported cases in regions where this infection is not endemic.”

A group of Czech and Slovak scientists, working in cooperation with the Alaska Department of Fish and Game, in 2013 went looking for salmon infected with this parasite. They examined 64 fish from Southcentral Alaska and found tapeworms in many of them, including one with the Japanese broad tapeworm.

It was a pink salmon pulled from Resurrection Creek near Hope, just across Turnagain Arm from Alaska’s cities. The tapeworm inside  was “found unencysted, deep in the musculature of the anterior part of the fish near the spinal cord,” the scientists reported. “It was highly motile.”

It was also the first Japanese broad tapeworm found in an Alaska fish in the wild. The parasite had been thought to be limited to northeastern Asia where a couple thousand people have been known to have been stricken by the parasite, which is far from the only tapeworm found in salmon.

Hidden dangers

“Diphyllobothriosis, a human disease caused by tapeworms of the genus Diphyllobothrium, is the most important fish-borne (disease) caused by a cestode parasite. Up to 20 million humans are estimated to be infected worldwide,” Tomas Scholz and colleagues reported in Clinical Microbiology Reviews back in 2009.

They noted 14 species of “broad tapeworms” or “fish tapeworms” that can make people sick, and they cited Alaska and Finland as places where parasite-related illnesses were high but appeared to be declining.

That might now have changed given the growing interest in eating raw fish, and the surprising number of Alaskans unaware of the potential downside given that Alaska salmon have been cited as one of the most common carriers of tapeworms of various sorts.

As long ago as 1985, the Oregon State University Extension Center was warning seafood retailers of the problems with parasites in wild salmon.

“…Fish that spend part of their life in freshwater such as salmon may carry Diphyllobothrium tapeworm larvae,” they warned. “These small, whitish, and somewhat flabby worms are common in salmon from some areas of Alaska.”

Most Alaskans who’ve handled a lot of fish – be they commercial, sport, personal-use or subsistence fishermen – have run into these small, whitish and somewhat flabby worms at some time.

YouTube these days has quite a collection of wormy salmon videos. Here’s one featuring wild sockeye salmon from Costco, and another of a live worm in “cooked” (obviously not cooked well enough) wild coho salmon from Whole Foods, and yet another worm in “rather pricey fresh wild pacific salmon fillets from a high-end fish market.”

The good news is that these worms won’t hurt you unless you eat them live, and even then they might not be a serious problem.

“Swallowing a live nematode larva can cause severe gastric upset called anisakiasis. This happens when the nematode attaches to or penetrates the intestinal lining. Nematodes do not find humans to be suitable hosts (however) and will not live longer than 7-10 days in human digestive tracts,” the Oregon paper said.

But it also warned that “swallowing live tapeworm larvae can cause a tapeworm infestation. The tapeworms may live in the human intestinal tract for several years. Symptoms can include abdominal pain, weakness, weight loss and anemia. Doctors successfully treat tapeworm infections with medicines,” if – of course – the condition is properly diagnosed.

Best news

Now, for the really good news. There are two simple ways to avoid problems with any of these parasites.

Number one: Cook your fish to an internal temperature of 140 degrees.

OK, so you don’t like overcooked salmon.

Number two: Put your fish in the freezer until they’re frozen solid and leave them there for a week. Or, if you’ve got a cold enough freezer – minus-31 degrees or colder – you can kill them in 15 hours, according to the Food and Drug Administration. 

The FDA also says flash freezing at minus-31 degrees or colder and then storing the fish for 24 hours at minus-4 degrees or colder will work.

“Brining and pickling may reduce the parasite hazard in a fish, but they do not eliminate it, nor do they minimize it to an acceptable level,” the federal agency cautions. “Nematode larvae have been shown to survive 28 days in an 80° salinometer brine (21% salt by weight).”

So if you’re going to cold smoke the fish or make ceviche, it would be a good idea to freeze the fish first. And the same for any salmon intended for that sushi.

As for that first, fresh salmon of the season that Alaskans so much love to toss on the barbecue, well, there is one thing on which all the authorities agree: Cook it well. It might not taste as good as that filet that still has a hint of red inside, but it is a lot safer.

And you can always put some of the fresh salmon down in the freezer for a week and still have it essentially fresh the next week. Think of it as “aging,” as with wine.

If nothing else, it might make life better in the kitchen. Even if you know that worm crawling out of your salmon won’t kill you, and even if you are well aware cooking will kill it and any others still in the salmon flesh, small, whitish and somewhat flabby worms slithering around on your fish are just not very appetizing.

Unless, maybe, you’re a serious survivalist.
















19 replies »

  1. Pete, it doesn’t matter if salmons are capable of abstract thought or not. Harming a human who is incapable of abstract thought is still wrong. Salmons, as with all animals, have a strong will to live. It should be plain to any reasonable person that they do not want to be caught or killed.

    Anthropocentrism causes a faulty view of the natural world. Case in point: Needlessly harming someone is not respectful of them, regardless of their species and no matter how tasty one may consider them to be. Ethics over appetite, especially harmful appetites. Close your mouth and open your mind.

    • Thanks for sharing, Mary. Good luck with your crusade. Alas, you have failed to convert me. If you really want to convert the world to veganism from your basement in Maryland, you might want to rethink your sanctimonious tone and acknowledge that some of us live in places where chia seeds and “vegan versions” of reality aren’t available. Best wishes! Oh yeah, you probably shouldn’t come to Alaska, after all. We have these things called mosquitoes and they have a strong will to live. Needlessly harming them is not respectful. Right?

  2. I haven’t referred here to anyone as being a “murderer,” Doug, but if that has occurred to you it indicates that you may be feeling guilty about causing needless harm to these (and other) animals. If so, it is to your credit in that it shows that you have a conscience.

    I also not referred to fishes as being “people.” I have explained the logic of why they are someones and not somethings, which has not been refuted.

    All I can do is point out the truth and appeal to people to do the right thing: not cause needless harm to our fellow sentient beings. It’s up to each individual to do the decent thing by not engaging in or supporting such animal abuse.

    Engaging in environmental causes is all very worthwhile, and I do, but first and foremost we should strive to not directly cause needless harm to others with our own daily actions, such as by not needlessly harming animals for food or ‘fun.’ Animal production/meat consumption and fishing are two of the most environmentally harmful activities that humans engage in. Environmentalism should start with ourselves if we are not to be hypocritical.

  3. Mary are you ok uprooting a healthy plant to feed yourself, or do you only eat fruits/veggies, etc. that can be harvested without harming the plant?

    • Thanks for your interest, Todd. Unlike animals, there is no credible scientific evidence that plants are consciously experience fear or pain or anything else. However, I do believe we should respect plants, too. By consuming them instead of animals we kill far fewer than if we were to consume animals, too.

  4. don’t be silly. salmon come back to Alaska only to die. D-I-E. it’s a the natural end of life. i’m happy to sometimes help them out with a quicker, less painful end than that for which they are destined. i do sometimes feel a little guilty about denying them that one, wild, orgasmaitc blowout just before the end, but sometimes life isn’t fair. enough with the vegan nonsense and toxin scares. the former just encourages a human population explosion, and the latter fails to recognize the world is full of toxins. they’re everywhere. the question with salmon and other fish/animals is whether they bioaccumulate those toxins to a significant extent. there is no evidence wild Alaska salmon do. the evidence is the opposite. if you handle them properly, they are one of the healthiest things you can put in your body.

    • By your logic, it would be okay to kill old people, including non-consenting ones. That life isn’t fair doesn’t justify treating others unfairly.

      There’s nothing nonsensical about veganism, which, in contrast to your assertion, is largely concerned with curbing human population.

      Alaskan salmon might not be as contaminated as some other fishes but that is damning with faint praise, and Alaskan waters aren’t so pristine, either. See, for example:

      Don’t delude yourself, they are far from “one of the healthiest things you can put in your body.” You can eat something (rather than someone) else. Leave the fishes alone, and for the animals who genuinely need to eat them.

      • And if we follow your logic, we have no old people to kill. The human life span shrinks rapidly when we stop using modern medicine to murder other life forms. But I do have to agree with you on one thing. Alaskan waters aren’t so pristine. Little is. The world is follow of contaminants natural and man made. It’s wonderful you think salmon a someone. I sure you believe that makes you holier than the rest of us. It doesn’t, but I will stop eating salmon the day they reach “someone” status. Until then, I’ll be what humans are, “the animals who genuinely need to eat them,” as you put it. Salmon have been a main source of protein for that Alaska animal for thousands of years.

      • Mary,
        You appear to live in Maryland. And I mean that in more ways than one. Your posts reek of ethnocentrism in the same way that the banks of the Kenai River reek of salmon carcasses every fall. Have you ever been to Alaska? If not, consider yourself invited. Come on up, spend some time with the fish and the people who catch them. This sort of emic perspective may open your eyes to the fact that there are different cultures with different belief systems and, yes, different diets based on locally available resources. Believe it or not, not everyone wants to live in Mary-land. Hope to see you soon!

  5. An informative article although you omitted the simplest way to avoid consuming these parasites, along with a host of other health hazards: By not consuming fish. That way you can also avoid the mercury, dioxins, PCBs, and other toxins, cholesterol, saturated fat, etc. Even if the parasites are killed, do you really want to eat dead parasites?

    All of the nutrients derived from fish, and from animals in general, can be obtained more healthfully, humanely, and environmentally responsibly from plant sources. Much of the food that most people eat is derived from plants, and there are marvelous vegan versions of virtually every type of food imaginable, including seafood:

    • Mary: thanks, but there is no vegan equivalent to a nice filet of salmon. sorry. not even close. and the Omega 3 benefits of eating fish, especially Alaska salmon, are well documented: they have lots of healthy fat, and being short lived creatures they contain very low levels of any toxins. they come back to Alaska only to die after a few years at sea, you know. i don’t mind tasty baked parasites. i worry more about the e-coli in the salad.

      • Craig, I doubt you have even tried vegan ‘salmon,’ so how would you know? Try it, you might love it! Many do, and it is increasingly popular. Besides, there are other things to consider beyond indulging a mere appetite, especially a harmful one. Salmons live long enough to accumulate plenty of toxins (and the oceans are, sadly, far from pristine).

        We can easily obtain omega 3s more healthfully from plant sources. Rich ones include walnuts, flaxseed oil, flaxseeds, chia seeds, hemp seeds, and, for a concentrated dose, algae supplements – algae being how fishes obtain their omegas.

        Salad ingredients can be cleaned prior to consumption. Any contaminants on them are external (and you can largely thank animal agriculture and the pathogenic manure used as fertilizer for E. coli contamination). Flesh pathogens, in contrast, are primarily internal.

        The bottom line is that if we don’t need to harm sentient beings -and science has shown fishes to be sentient- why do it? Needlessly harming animals for food or ‘fun’ or any other reason is animal abuse: plain, inhumane, and unjustifiable.

    • “And if we follow your logic, we have no old people to kill. The human life span shrinks rapidly when we stop using modern medicine to murder other life forms.”
      My concern is with sentient life, which bacteria and viruses are not known to be. Additionally, i do believe in self defense.

      “It’s wonderful you think salmon a someone. I sure you believe that makes you holier than the rest of us. It doesn’t, but I will stop eating salmon the day they reach ‘someone’ status.”
      It’s not merely that I think they are, they plainly are. Inanimate objects are “things.” Animals, including humans, are not things, rather they are someone.

      “Until then, I’ll be what humans are, ‘the animals who genuinely need to eat them,’ as you put it. Salmon have been a main source of protein for that Alaska animal for thousands of years.”
      There may have been a time when humans needed to eat animals, and there are some people who genuinely still do. However, that is no longer the case for the vast majority of us, and by doing so we deprive those who genuinely do need them of their sustenance.
      Per the Academy of Nutrition and Dietetics, “the United States’ largest organization of food and nutrition professionals”: Well-planned vegan diets “are appropriate, and they satisfy the nutrient needs and promote normal growth at all stages of the life cycle, including pregnancy and lactation, infancy, childhood, adolescence, older adulthood, and for athletes…Vegetarians and vegans are at reduced risk of certain health conditions, including ischemic heart disease, type 2 diabetes, hypertension, certain types of cancer, and obesity. Low intake of saturated fat and high intakes of vegetables, fruits, whole grains, legumes, soy products, nuts, and seeds (all rich in fiber and phytochemicals) are characteristics of vegetarian and vegan diets that produce lower total and low-density lipoprotein cholesterol levels and better serum glucose control. These factors contribute to reduction of chronic disease.”
      Tradition is no excuse for abuse.

      • Mary: It’s senseless to continue this discussion because in the end your argument is inherently illogical. Simply by occupying space on the planet we displace, and thus eliminate, other creatures. The only way to avoid that is to be gone from the planet. All the rest of it, whether we like it or not, falls into that grand scheme of that thing we call nature, which is driven by two fundamentals: life and death. I enjoy being part of nature. I like the feel, touch, smell, blood and taste of it. You obviously like something else. That’s fine, but this has no become as senseless as debating whether there is a God or Christianity versus Hinduism.

    • Pete, your post reeks of anthropocentrism.

      I can appreciate someone using indigenous methods to live a subsistence lifestyle, but by and large that is not what is happening there. Culture is no justification for animal abuse. Genuine civilization entails respecting nonhuman animal members, too, as is increasingly being recognized by cultures around the world.

      Everyone may not want to live in Maryland (or “Mary-land”) but everyone wants to live, including nonhuman animals. Respect our kin: Live and let live.

      • If it is senseless to continue the discussion, Craig, it is because your mind is closed. True, we displace other animals simply by living on the planet but that doesn’t mean we shouldn’t try to minimize doing so. Consuming a plant-sourced diet is one of the most effective ways we can do that.

        I love nature and revel in it. However the love of nature doesn’t justify causing needless harm to sentient beings, be they human or other. True love of nature entails respect and appreciation of life, not cruel exploitation of it.

        Religion is based on faith. Veganism is based on fact, reason, and compassion.

      • You’re not going to convince anyone to stop eating fish by calling them murderers, or by any “fish are people too” argument. If you really want to save the fish in Alaska, you might have more luck by looking into the Pebble Mine controversy and getting involved there.

      • Mary,
        You say anthropocentrism, I say anthropomorphism. You have no idea what salmon “want”. What they are genetically programmed to do is survive long enough to reproduce. Do you truly believe salmon are capable of abstract thought? Can you show me the data to back up such a claim?Anthropomorphism leads to an inaccurate understanding of biological processes in the natural world. Respect? Most Alaskans I know have tremendous respect for salmon. Many consider them sacred. They also eat them after giving thanks. Yum!

Leave a Reply