07 August 2016

Why you should never eat raw fish.

Why you should never eat live (or dead) raw fish

Before I go any further, I admit I love sushi. But so far, all I’ve eaten is squid and shrimp sushi. I’ve never had the courage to try raw fish sushi.

Why? It’s because raw fish are already being eaten. From the inside. By parasites.

Several years ago I heard of an idiot who was fishing with some of his idiot friends-and of course, drinking beer. The fishing was no good, they were bored out of their skulls, and, now, being drunken idiots, they decided to dare each other into eating the live bait.  Who had the ‘courage’ to swallow a live minnow? C’mon, what could it hurt; they were drinking BEER, right? Alcohol kills everything, right?
Such is the reasoning (or lack thereof) when one is drinking while male.

One man, perhaps all, did. He downed a few live minnows and of course, was the man of the hour.
I bet they all forgot about it for a while. Until The Man got sick.

He finally went to a doctor who found that he had tapeworms. In his BRAIN.

The minnows had been infested with tapeworms. The tapeworm larvae had not been killed by his stomach acid (or the beer). Of course not. Any parasite that’s life cycle is meant to be inside a critter won’t exist for long should it be easily killed by stomach acid. Oh, heck no. Usually a tapeworm that has evolved to parasitize fish instead ends up in a warm blooded mammal, it doesn’t die. It gets lost. It (or they) wander about and sometimes end up in places like one’s lung, or eyeball. Or brain.  That’s where they found Mr. Minnow’s tapeworms. In his brain.

Here’s an X-ray of a Chinese man who is absolutely LOADED with tapeworms after a long period of time eating sashimi (raw fish). 

Before you think it’s a one off occurrence, understand that virtually every living thing has a parasite evolved specifically for it. A case could be made that parasitism drives evolution. Read Parasite Rex by Carl Zimmer if you want to know more about that.

The current belief is that cooking or freezing raw fish will kill parasites. That’s true, to a degree. But it isn’t foolproof. A study of flounder infested with Anasakis simplex, a nematode commonly found in infested fish (and humans who eat them raw), found it could survive microwaving at lower temperatures. (i.e., half power). Roasting temperatures below 77 Celsius (~165 F) weren’t reliable in killing them, either. Freezing at 0 C (32 F) for 24 hours was good enough to kill them.

Anasakis causes a great number of human infestations in countries and cultures that routinely consume raw or lightly ‘cooked’ fish. Japan, of course, provides 90% of these cases due to the consumption of sushi and sashimi, but Spain (ceviche), the Netherlands (marinated herring) and Scandinavia (smoked fish) all rank high in infestation cases and resulting illness. Even the US, where sushi consumption is common, is seeing an increasing number of cases of illness.

Why do I bring this up? In January, I started up a freshwater aquarium. I stocked it with Amano shrimp, a fresh water shrimp from Asia, and dwarf neon rainbows, a lovely fish from New Guinea.

12 weeks later, almost to the day, I found one of the six fish dead. I took it out of the tank and put it in the trash. Before I did so, though, I noticed it had two little red threads protruding from its anus. I trashed it and almost forgot it-until a few hours later. The
 the biologist in me woke up and wondered, what killed this fish? This tank is fully cycled and well balanced, nothing else is sick. One day the fish was fine, then next, dead. Why is it dead?
Several hours later, I retrieved the dead fish from the trash. This time I saw NO red threads. Hmmm. I put it in the freezer, intending to dissect when I had a little time.
It had been in the freezer for about an hour when I put it under my dissecting microscope.

There was a little red spot at the anus.

I opened the dead fish. It was full of red worms. LIVE red worms. Not only alive, but vibrantly so. I could see the blood coursing back and forth along its intestines (as the worm was transparent.) They literally crawled out of the fish’s stomach, trying to escape the glaring light. This little monster is Camallanus.I believe the fish had it -or contracted it-when I got them from the local fish store, but it could also have been brought in by the shrimp, who can serve as an intermediate host.

The fact that they had been in a dead fish, then a dead fish out of water, then a dead fish in a freezer, made no difference to the worms. I believe had I dropped them back into the tank they would have been fine.

Now I know all my fish are infested with this nematode. You can see the females protruding from the anus of a fish, laying its eggs. Its life cycle is 12 weeks. Once it’s in your tanks, you are screwed. All of your fish will get the parasite. Everything that has had any contact with any water from the tank is contaminated with the virtually invisible eggs. 

  I had to humanely kill one of the fish today. You could see the adult female worm routinely extruding from the fish’s anus, laying her eggs in the water. I couldn’t catch her to kill her and I didn’t want to stress her by chasing her. It’s a big tank and a small fish.

She had stopped eating. When I caught her today during a water change, she didn’t race so hard. It was easy to catch her. She was tired. She was thin, so thin it’s hard to imagine how she lived for so long. Poor little thing.

By the way, NEVER EVER flush an unwanted, a sick or dead fish down the toilet. That’s how these parasites-originally from Asia-establish themselves in North American waters in the first place, and why our rivers and lakes are full of carp. Folks got tired of the kid’s goldfish and flushed them, never dreaming they could survive. They do. I am sorry to say, they do.
(For that matter, never dump an aquatic pet of any sort into any body of water. It’s how invasive species get into them, critters such as red slider turtles that have completely eradicated our native turtles…by overtaking their habitat and reproducing like crazy.)

After I killed her (a swift decapitation), I opened her up.

There was nothing in her. Not a lick of flesh. All her muscles and flesh were gone. . She was literally skin and bones…and worms. The little effers were alive and well.
Not anymore. I took a few pictures and here is one of the best:

Here's a close up of this nightmare:

I put the fish in the trash…along with the devil worms. It’s only a matter of time before I have to kill the rest, but for now, they look fine, although I’ve seen a worm protruding from one’s anus. They’re too healthy, at the moment, to catch. But as the number of necessary hosts drop, and the number of parasite worms eggs grow, it’s only a matter of when, not if.

These nematodes are piscine specific, meaning they apparently  can only survive in fish. But, as is always the case in biology, you can never say never. You cannot even say “generally speaking.” That’s how evolution works…one out of a thousand worms manages to survive in a new and utterly different host. It’s like landing on a deserted island. They have free rein to evolve and explode in numbers because they have no competition, and the host’s immune system has no knowledge of this completely alien creature, so it leaves it alone. 
 Now that I know that these little effers are in all types of freshwater fish (because someone flushed a sick or dead one), and that salt water fish have either the same or related nematodes (or other monsters) fish, I won’t ever eat sushi again.

What are your chances of eating one of these parasites? Probably pretty good, but they’re probably dead, if you haven’t eaten the fish raw, freshly dead, or whole. 
Do you have one of them in you? Probably not. For now. But as more people (we’re up to almost 8 billion now?) eat more fish, as more of the more popular species go extinct (i.e. tuna), we will find ourselves eating lower down the food chain. Species that were, up until now considered “trash fish” and were used solely for bait, will suddenly end up on our tables because the desirable species are gone. Parasites that, up until now, were manageable because there were millions of fish in the sea, now find themselves having to settle for the handful of ‘trash fish’ as that’s all that is left. 

Climate change is warming the oceans, conditions that are favorable to parasites due to more stress on a fish’s immune system. Fish that can tolerate worsening seawater conditions (i.e. pollution or acidification) are more likely to be infested, again, due to a stressed immune system. Improper cooking of raw fish doesn’t kill the parasites. 

So. Freeze that fish hard, and cook it thoroughly. Don’t eat the guts, in other words, don’t eat a whole fish. Tapeworms encyst in muscle but high heat kills them. But, as I proved, intestinal fish such as Camallunus can survive for a very long time…days, perhaps, in a dead fish. And if it finds itself in you, it may just like what it finds.

Sorry to say, but sushi is probably  going to have to go by the board. I’m sorry.

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