3-Pound Goldfish Found—How’d It Get So Big?

As an avid fisher for 20 years, Mike Martin has his fair share of stories. Many fishers can tell tales of the one that got away, but Martin’s latest yarn is all about the one he reeled in earlier this month on Lake St. Clair (map), just north of Detroit, Michigan.

“Basically, I was doing what I always do, trying to catch perch, and I thought I had a big perch on. Um, definitely not a perch,” Martin told WDIV News, the NBC affiliate in Detroit. (Watch a video of the giant goldfish on KSDK.com.)

A 15-inch goldfish named Bruce is lifted from the water at a fish farm in Dongguan, China, in 2002. Photograph by Bobby Yip/Reuters

Indeed not. On his hook was a 15-inch-long (38-centimeter-long) goldfish that tipped the scales at 3 pounds (1.4 kilograms). Compare that to an average aquarium goldfish that generally measures just a few inches—their breeds come in a wide variety of sizes—and it doesn’t take long to figure out that this whopper of a fish is going to need a bigger bowl. (See a picture of a see-through goldfish.)

That begs the question: What exactly is a goldfish, and how can they get so freakishly big?

Goldfish: Carp in Pretty Clothing

Goldfish are actually a type of domesticated carp. Almost 2,000 years ago, the ancient Chinese began to domesticate Prussian carp, Carassius gibelio, for food and as ornamental fish.

Over time, mutations creating orange, red, and yellow colors began to emerge in the dull-colored Prussian carp, creating the coloring we now associate with goldfish. The fish was transported to Europe in the 1600s and to the United States in the 1850s.

Although not naturally found in the wild, goldfish have occasionally been found in ponds, lakes, and streams. Most researchers believe that these goldfish were either dumped there or somehow escaped from the “porcelain express” after being flushed down the toilet.

Many of the unusually massive goldfish—like the one Martin caught—have been found in these outdoor settings, but goldfish experts say it’s a myth that a large tank will yield large goldfish. (See pictures of the world’s monster fish.)

Big Fish in a Small Pond

To grow a big goldfish in a small pond, breeders focus on two main factors: food and temperature, according to Tropical Fish Data, a database on tropical fish. A high-protein diet is generally thought to increase the body weight of a goldfish, as is being fed more food, more often.

Warm water also increases a goldfish’s size. Goldfish kept in outdoor ornamental ponds generally grow quickly in summer and little, if at all, over winter. Keeping goldfish in a heated aquarium allows them to maintain their summer growth spurt year-round.

The longest known goldfish, according to Guinness Book of World Records, measures 18.7 inches (47.4 centimeters) from nose to fin and belongs to Joris Gijsbers of the Netherlands. Guinness did not have any official recordings of the fish’s weight, so it’s unclear if the Dutch goldfish beat the new Lake St. Clair goldfish in bulk as well as length. (Also see Biggest Great White Shark Caught, Released.”)

Martin hasn’t purchased a swimming-pool-size fish tank for the goldfish he caught, nor is he hosting a neighborhood fish fry. Instead, he’s currently keeping the specimen in his freezer—he ultimately intends to mount it on his wall.

Carrie Arnold is a freelance science writer living in Virginia. When she’s not writing about cool critters, she’s spending time outside, drinking coffee, or knitting.

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Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at http://www.carriearnold.com