A Staff Report from the Straight Dope Science Advisory Board

Is that black line down the back of a shrimp what I think it is?

October 19, 2000

Dear Straight Dope:

OK. this may be gross, but I feel the need to know the truth before I eat another shrimp! That black line down the center of its back … is it a "waste chute" for excrement or is it a vein of sorts that is part of a a circulatory system? I swear I have tasted "grit" if it isn't completely cleaned out, but my friend says it is not poop. What gives?

SDStaff Hawkeye replies:

They say the truth is ugly, but they forgot to mention that sometimes it's also disgusting. I mean, I've heard of a crab log, but a shrimp log is something entirely different. The absolute straight dope is that the black line found in most shrimp is its intestine. And yes, sometimes that puppy is so full as to threaten to practically burst, taking out the shrimp and anything within several inches of it. Not a pretty sight, but welcome to the shadowy trenches that lie between science and journalism.

To be accurate (and this is the Straight Dope, after all), the black stuff is the contents of the intestine and not the intestine itself. If you've ever spent any time preparing shrimp, you would know that after tearing off their heads, ripping off their shells, and then eviscerating their little corpses, every so often you come across one without the dreaded black tract. That's because the actual colon is a transparent tube of cells and that particular shrimp's colon was empty. More demonstrable evidence can be found in those shrimp whose intestinal contents are incomplete; sometimes that little black line looks more like a sequence of dots and dashes instead of one long continuous line. Yet, when you remove one, it all comes out, held together by a nearly-invisible strand.

There are several reasons for removing the intestine, the most obvious being the aesthetic appearance of the poop chute (I mean, how can you NOT look at it?!). In addition, the shrimp's colon and its contents can impart a disagreeable taste and gritty texture to the meat or dish.

What is that grit? Dirt, mostly. If you've ever had occasion to chew on something with even one grain of sand, you know that the grain feels like a pebble in your mouth. Generally speaking, however, you'll find decayed vegetation and decomposing bits of dead animal. Sorry, but most shrimp are scavengers, acting as Nature's garbage disposals. Vegetarianism is sounding better by the minute, I'm sure.

Calling that black tract a vein isn't exactly true, but it's not exactly wrong, either. The shrimp's dorsal vein runs alongside the intestine, so unless you're a crustaceal surgeon and can remove the vein without removing the intestine, you shouldn't waste your breath complaining about it.

Is shrimp doody safe to eat? Yes, but the shrimp should be cooked thoroughly. Otherwise, you may experience problems with your own digestive tract.

Shrimp colon is far from the grossest form of seafood. Ever heard of ama ebi? It's a type of sushi that presents a raw prawn on a small block of seasoned rice. The little morsel is deheaded, peeled, and deveined. Still hungry? Ebi odori ("dancing shrimp") uses a prawn so fresh it's alive. The Japanese regard this is a rare treat. To be served properly, it must be prepared so quickly that it reaches the table still twitching. Be still my stomach.

A final tidbit:  In Europe, the first native variety of shrimp to make its way from the fishing net to the dinner plate was Crago vulgaris. This particular species is fairly small, so the new tasty shellfish was called schrimpe, the Middle English word for "small, puny person." Thus, the insult predates the food! Since some species of shrimp can grow to 15 inches in length, the old oxymoronic joke about "jumbo shrimp" owes its origins to its etymology and not some comedy routine.

Next time, please limit your questions to something a little less disturbing, like chocolate, OK?


  1. Detrick, Mia. Sushi. Chronicle Books, 1981.
  2. Rombauer, Irma S., Marion Rombauer Becker, and Ethan Becker. The All New All Purpose Joy of Cooking. Simon & Schuster Inc., 1997.
  3. Henrickson, Robert. The Ocean Almanac. Doubleday Publishing, 1984.
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