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Friday, September 22

Parasites in Fish, Part 1 -- Cod worm

If you've been reading this blog for the past couple of months (or even days), you probably came to expect something appetizing from it. Well, I have news for you folks. The next few posts might shatter your perception of Beyond Salmon for I am embarking on a "Parasites in Fish" series and there is no way I can make this lovely topic appetizing.

Why has a girl that almost flunked biology in high school got so interested in parasites? Sushi of course! Oh, and tartar. And ceviche, too. It’s amazing what I’ll do for raw fish. I've been buying tuna, salmon, and branzino from New Deal to serve raw for over a year and when I tried to go back to restaurant sushi recently, I realized that I've been spoiled for life. New Deal's fish is just better. The question is how much of a risk am I taking by serving raw fish at home?

If you are a squeamish person, new to cooking fish, I suggest that you don't read any further. I had a woman, in one of my classes, tell me that she wouldn’t eat fish again after my little lecture on parasites, and I don't want to be responsible for people stopping to eat fish purely because of squeamishness. If you are cooking the fish (with heat), no harm will come to you. I promise.

No mater how hard I looked, it was hard to find solid information on this topic. FDA was passionate about scaring the media, and the media was passionate about scaring the consumers. What I needed to find was someone passionate about parasites, and after 20 unsuccessful Google queries, I finally figured out what to search for: "parasitology Ph.D." Yes, there are people who care about parasites as much as I care about food and after a few e-mails, I had interviews lined up with 2 prominent parasitologists, Dr. Palm from Institute for Zoomorphology, Cell Biology and Parasitology in Düsseldorf, Germany and Dr. Gardner from Harold W. Manter Laboratory of Parasitology at the University of Nebraska.

First of all, let me say that parasitologists are some of the kindest and most patient people I have ever met in academia. They were willing to explain fish parasites in terms that even I could understand and painstakingly answered all my questions. I learned that there are over a hundred species of parasites that can be found in fish, but only 3 of them are potentially harmful to humans: Pseudoterranova decipiens (a.k.a. “cod worm” or “seal worm”), Anisakis Simplex, and Tapeworm.

Today, our special guest will be cod worm. I remember my first encounter with this critter about 4 years ago. As I unwrapped a cod fillet, I was greeted by a little worm squirming out of the fish. Good thing I heard about these worms before, or I would have thrown the fish in the trash and never set foot into that fish market (actually, it happened to be Whole Foods). In spite of my initial disgust (I am the kind of person who screams at the sight of an itsy-bitsy spider), I inspected the fillet, removed the worms and cooked the fish. It tasted just fine, and as you can see, I lived to tell the tale. These little worms are the pain of any fishmonger's existence because they freak the hell out of consumers. They are particularly common in white fish (cod, haddock, flounder, sole, and halibut), but I've also seen them in swordfish and monkfish. How often do you see them as a consumer? I cook fish at least 3 times a week and I'll see them a few times a year.

To prevent us, consumers, from having to look at these unsightly animals, the fish processors put all white fish through a process called "candling." They put the fillets on glass sitting over a lamp. This allows them to see through the fillet and remove any visible parasites. Think about this process as an airport inspection -- it makes everyone feel better, but it's not full-proof. On occasion, a few worms can escape the inspection and travel from the fish processing facility to your fishmonger and then to your kitchen. If this happens to you, don't panic. Remove the worms, and cook your fish the usual way. If you don't want to cook your fish after seeing the worms, I quite understand. Just don't go out of your way to ruin the fishmonger's reputation. The presence of worms has nothing to do with the freshness of the fish and I assure you that your fishmonger tried his or her hardest to protect you from this terrible experience. Last thing they want to happen is for you to find worms in your fish, but unfortunately this does happen sometimes.

What happens if you eat a cod worm? If it's dead, which it's bound to be if you cooked your fish to opaque state (or 140F), nothing at all happens. Even if you prefer your fish cooked a little less (120-130F) like I do, the odds of you eating a live worm are very slim. It would have to be a really hardy worm to survive those temperatures. If you are serving fish raw, and one of those guys manages to stay intact after you sliced the fish, and makes it all the way to your tummy intact, you are in trouble. Your stomach will eventually kill them, but since they originate in seals, they can get quite comfy in any mammal including us humans making the experience extremely unpleasant. As Dr. Palm puts it, “It is better not to eat them alive.”

What does this mean to serving fish raw or cured? That’s a topic that deserves its own post, so stay tuned.

You might also want to see these Frequently Asked Questions that people ask me about cod worms.

p.s. On a happier note… I’ll be away in California on vacation starting tomorrow, but I look forward to responding to all your questions and comments and telling you more parasite stories when I get back.

Posted by Helen at 8:21 PM

27 comments:

5penny said...

Hi, I came from simply recipes for the pate brisee advice and am staying for the parasite stories. I'm not really a huge fish eater, but I apparently am my grandmother as I now prefer to read about food preparation, haha. Insightful and delicious site!

2:49 AM

ilva said...

Great and interesting topic, it's important to learn about these things as well. I'm quite squeamish but I prefer to know about the dangers and how to deal with them! Thanks Helen! I hope you are enjoying California!

3:50 AM

Magda said...

It takes a passionate and talented writer to turn a lesson on parasites into something that reads like a detective story! I can't wait for the next installment.

And, lazy cook as I am, I made the carrot stuffing for eggplant last night and it's wonderful! I'll do the eggplant today. Thanks!

4:06 AM

Michele said...

What might happen IF one did happen to survive and take residence in your stomach?

10:52 AM

Amy said...

Oh I wish I hadn't read this just now. Any other time, I would have wanted to know more about parasites in fish, but I am making seared tuna for dinner. I might have to have an extra glass of wine. Cheers!

6:19 PM

Dianka said...

Wow, what an important topic, given that we eat fish more and more these days. You never can be too careful! Have fun in California!

3:16 PM

tsduff said...

I live here in sunny California, and once I ordered sushi to-go at a high-end sushi restaurant. Inside, I had been served a piece of tuna with a wriggling, very narrow (like a pin) pink worm. I don't know what kind of worm it was, but obviously it grossed me out and I threw out the entire lunch. I have never been back to that eating establishment. It seems to me you would see a worm in the fish while slicing it for nigari! I still adore fish, and eat it all ways, including raw. I just look carefully before taking a bite! Good post.

6:12 PM

shawn said...

Oh, definitely such a diversion. But don't worry, I'd still read all of your parasite series. It's more of the learning actually that I'd stumble upon your blog once in a while. Keep it up!

10:12 PM

veuveclicquot said...

wow. that was instructive. thankfully i'm not squeamish!! looking forward to learning more about this topic.

hope you're having a blast in california!

11:37 AM

Culinarily Curious said...

I'm also new here, and as a sushi and rare-fish lover, I'm going to get as much if not more out of your parasite series as your more appetizing topics. Thank you for taking the time to share your knowledge with us.

12:58 AM

Duane said...

That's creepy. But it won't stop me from eating fish. I may think twice before eating any raw fish though.

4:14 PM

Anonymous said...

Haven't experienced cod worms yet, I may well avoid cod but I actually don't order it very often (I get dried cod more often than fresh).

Like your blog.

7:20 PM

Stephanie said...

Helen, very useful post, thanks. Is there a specific way you remove them? I'm thinking of ticks, how you light a match on their rear end so they scramble out instead of ripping them off and leaving their head buried in. Or like the method of removing a leech (yes, I know that from personal experience too). How did you remove the worms? Just a pair of kitchen tweezers like you use to remove pin-bones?

9:39 AM

Anonymous said...

I love fresh fish and food! However, when i went to the supermarket today in the UK and bought some fresh cod i was disturbed to see the end of a worm wriggling inside the cod! I normally am sqeamish but this time i was intrigued! I called the supermarket straight away and they said cod worms were common and just to cook the fish thoroughly. I was not convinced! Hence, searching for more info landed me on your blog! Satisfied customer now but still questioning whether i should take it back to the supermarket or just enjoy the cod (without the worm, of course)! Thanks again!

3:47 PM

Helen said...

Hi Anonymous,

Most supermarkets in US will gladly exchange the fish or give you a refund if you found a worm in it. As you probably have already learned from the article, the worms are not in the fish because it's not fresh. Friends of mine who go fishing told me they found them in fish that was just pulled out of the water. Your supermarket is correct that if you cook the fish through, they are harmless to your healthy. Don't get carried away with "cooking it through." 10 minutes per inch of thickness at 450F will be sufficient. But I know what you mean about them being just plain ikky. Whenever I get them in my fish, I lose appetite too.

Cheers,
-Helen

4:15 PM

AMW said...

I think I am a cod worm magnet! I recently bought wild snapper and was greeted by a squiggling live worm upon opening the package. Disgusting! Then, after a month's recovery, I decided to spend even more money and taxi fare, and bought 2 large wild cod fillets. I just sat down to a big curly cooked worm in the flesh of my flakey perfectly cooked cod. I called the store and read them the riot act, then found your blog on my Google search. I don't want to throw out my fish, but I can't imagine eating it again this week. ICK! Thanks for your post.

8:20 PM

Helen said...

AMW,

I feel for you! Worms and fish are really icky looking. If you need a little recovery time before trying cod again, here are some normally worm-free fish:

-tuna
-salmon
-branzino
-orata (sea bream)
-baramundi
-trout
-tilapia

Cheers,
-Helen

10:43 PM

Anonymous said...

i found a 2cm long,pink/red worm in a fillet of perfectly well cooked cod.Was this a cod worm?i had no idea that worms could be found in the flesh of fish!

8:38 AM

Helen said...

Hi Anonymous,

Yes, you found a cod worm. Since the fish was cooked, you were completely safe to eat it (I mean the fish, not the worm.) You could of course eat the worm too, but I know few people who find them appetizing ;)

Cheers,
-Helen

8:45 AM

lafaz said...

Very interesting topic. I represent from a chilled tuna processing factory. I have seen a parasite in tuna which is invisible during candling but appear later on. We cant help in such situation.
What do you think about the Sashimi (raw eaten fish)? Japanese are so fond of sashimi and its getting popular in other countries too. The only preventive method is to blast freeze the fish before eating. Keep writing, Regards/Lafaz

12:08 AM

Helen said...

Hi Lafaz,

Welcome to Beyond Salmon. there is a ton of info here on serving fin fish raw, so browse around and have fun.

Here are some links to get you started:

Serving Fish Raw

Tale of Two Tunas

Cheers,
-Helen

12:25 PM

Maria said...

Hi: Found a 3 cm worm on a wild alaskan cod filet bought this Easter weekend from Costco. I feel extremely squeamish at the sight of one, especially when I love fish. I then called them immediately and was told that it is quite common in cod, and I could choose to eat it or return it. Well, I chose to return it and bought home a worm free Halibut filet.

2:36 AM

Helen said...

Hi Maria,

Switching cod for halibut -- I'll take that exchange any time :)

Cheers,
-Helen

10:05 AM

Anonymous said...

HI..MY FIANCEE JUST PULLED OUT A DARK LOOKING COILED UP WORM IN OUR SALMON....ITS ABOUT AN INCH LONG WHEN UNCOILED...THE FISH WAS BAUGHT FROM TESCOS IN A READY MEAL BOX THE KIND YOU TAKE HOME AND FREEZE AND THEN OVEN COOK IT WAS COOKED AT 200C FOR 35MINS ...SHE GOT LUCKY AND NOTICED IT BEFORE EATING IT BUT ME ON THE OTHER HAND EAT QUICKLY AND DIDNT LOOK THROUGH MY FISH AS I ATE IT..WHAT IF I ATE ONE ANYBODY NO WHAT KIND OF WORM IS IN THE SALMON AND IS IT DANGEROUS..THANK YOU

3:20 PM

Helen said...

Hi Anonymous,

All worms in absolutely all fish are completely harmless if the fish is cooked (yes, even if you ate a worm). So unless you are eating fish raw, you don't have to worry about them.

Cheers,
-Helen

3:44 PM

Marijhaa said...

Hey, I’m another Tesco’s fan on this blog! Yes, that was until I bought a couple of Mackerel fillets. They were infested with these skinny milky colour see-through one inch long coiled warms. That was extremely disgusting! Despite that I got my refund, I would still like to know if that is normal, as all warms described on this blog seem to look different. Cheers! PS: if this is to be expected when you buy fish, should there not be a warning on the package?

1:32 PM

Helen said...

Hi Marijhaa ,

There are hundreds of different fish parasite species and they all look different. What you found in mackerel is "normal", but that doesn't make it any less freaky for you I bet. Rest assured that this level of infestation is unusual and it doesn't mean that mackerel is normally wormy.

Why is there no warning on fish? Hmm, good question. I guess that it's because these icky creatures don't pose any danger if you cook the fish. Besides, would you buy fish if it had a warning on it about possible worms? I am not suggesting you cook this wormy fish just because it's harmless -- if you are disgusted, you won't want to eat it anyway. Returning it to the store for a refund is reasonable, just don't give them a terrible time about it. If the fish was sold whole, there is nothing they could have done to prevent it.

Here is an interesting comparison. This weekend I bought some lovely wild mushrooms. Chanterelles were fine, but morels were crawling with worms when I cut them in half. I was totally disgusted and asked my husband to help me remove the worms. He tried for a while, but then we realized that there are just too many of them and we threw all the morels out. I was not upset at the store in any way. When you buy wild mushrooms, you have to expect that to happen sometimes. And no, there was no warning saying "wild mushrooms might have worms" :)

Keep in mind that humans are not the only ones who like fish, mushrooms, apples, raspberries, corn, etc. There are plenty of living creatures that wouldn't mind getting there first and unless we get some serious chemicals involved, we have to put up with a bit of ickiness once in a while.

Cheers,
-Helen

2:25 PM

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