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Goldfish and Koi Mass

Some rules of thumb for measuring koi and goldfish weight.

By Stephen M. Meyer

Q. Many of your articles refer to the mass of fish in grams or kilograms. Most hobbyists, however, are unable to weigh their fish. All we usually can estimate is their length in inches. Is there some rule of thumb that relates length to mass?

A. About a year ago we published some graphs that showed the relationship between the length and mass of koi. Revised versions are reproduced here. Because the relationship between mass and length changes significantly once a koi exceed 16 inches, it is more practical to use two graphs to illustrate the data. Fortunately, the many varieties of koi have the same physical structure and therefore the graphs are quite accurate for all koi. The graphs indicate the range of weight for a given length, which is +/-15 percent of the average mass for that length.

Goldfish, on the other hand, vary too widely in body shape and size to successfully graph the relationship of mass to length. So, goldfish lovers will just have to get out their scales (no pun intended).

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Goldfish and Koi Mass

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Reader Comments

Carl    Livermore, CA

5/20/2013 11:24:45 AM

Fish mass is not an easy thing to figure as compared to length.

Nora    Wichita, KY

8/19/2012 1:46:33 PM

Good info, thanks!

cynthia    brownsville, TX

5/31/2012 9:14:52 PM

lol never get tired of reading this one

Dave    Erie, PA

5/10/2012 10:31:17 AM

very helpful thank you

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