How do they harvest caviar?

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Oct. 4 2005 6:07 PM

How Do They Harvest Caviar?

They suck it through a straw.

Mmm, fish eggs 
Click on image to enlarge.
Mmm, fish eggs

As of last Friday, the United States no longer permits the importation of fancy beluga caviar from the Caspian Sea. The U.S. Fish and Wildlife Service announced the ban as part of an effort to protect endangered sturgeon near Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. Do sturgeon die when fishermen take their eggs?

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

Yep. Almost all caviar is harvested from dead fish. Fishermen on the Caspian wait until the mature female sturgeon (which are at least 10 years old) are ready to migrate upstream and lay their eggs. Once caught, the sturgeon will be transferred to a large boat, where workers slit her open and remove her eggs. The caviar is cleaned to prevent spoilage and then packed up; the rest of the fish is sold for flesh.

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Why can't the fishermen postpone the harvest until the sturgeon lays her eggs? First of all, the eggs would be almost impossible to gather. A female that's ready to spawn might be swollen with pounds of black caviar clumped together on her ovaries. Once she releases these eggs into the water, they're much harder to collect, clean, and package.

Second, there's no market for ovulated or fertilized fish eggs. When the female begins to spawn, the exterior of her eggs deteriorates to allow for the penetration of sperm. Even if fishermen were able to sweep up those ovulated eggs, they wouldn't be able to sell them: An egg with a broken-down lining will eventually leak and turn to mush. (The quality of caviar depends on its firmness, taste, color, and size.)

Fish farmers who raise sturgeon for caviar sometimes use a surgical procedure to remove eggs from a female without killing her. To foster reproduction in captivity, aquaculturists will induce ovulation in a female with hormone injections and then make a small incision in her abdomen. Eggs that have already detached from the ovaries can be scooped out with a plastic spoon or squeezed out into a bowl.

Most farmers use this technique only to obtain eggs for insemination, but some Russians do live-harvest eggs for food. In some cases, a farmer might perform a Caesarean on a fish that hadn't ovulated. He could cut out some but not all of her eggs before sewing up the fish and putting her back in the water. A farmer might also induce ovulation, squeeze out the loose eggs, and then use a novel process to restore the integrity of their outer coverings.

Caviar producers who harvest from dead animals can still use surgical techniques to improve their yield. Some fisheries will test the eggs of a mature female before killing her. First, an incision is made in her abdomen and then a small tube is inserted. The farmer then puts his mouth on the tube and sucks out a small quantity of eggs for examination. If they're the right color and consistency, he'll kill the animal and harvest the caviar. If they're too "ripe"—if the fish has begun to break them down for reabsorption—he'll put her back in the water and wait until her next reproductive cycle.

Got a question about today's news? Ask the Explainer.

Explainer thanks Peter Struffenegger of Sterling Caviar, Frank Chapman of the University of Florida, and Mark Zaslavsky of Sturgeon AquaFarms.

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