Is that a big goldfish or a small koi? 

The fish in this Facebook photo remains a mystery.

Is a goldfish the "Loch Ness" of a small South Carolina lake?

Or is a small koi on the loose?

The identity of this fish remains a mystery.

Parks and recreation workers in South Carolina found what they're calling a nine-pound goldfish while electrofishing to gauge the health of a lake in Greenville. One fish didn't simply float to the top. Instead, it jumped out of the lake.

"It reminded me of when I was a little kid, my mom was a teacher and she brought a goldfish that was in a small fishbowl home. We put it in a bigger aquarium and we both were surprised (at) how big it grew," Ty Houck, director of greenways, natural and historic resources for Greenville County's Department of Parks, Recreation and Tourism, told USA TODAY. 

© Courtesy of Ty Houck/Greenville Parks, Recreation & Tourism County workers claim they found a 9-pound goldfish in a lake in South Carolina, though an expert from the University of Texas is skeptical.

This goldfish isn't native to the area, but they aren't invasive, Houck said. He and Scott Robinson, who was working with him, put the fish back in the water after they took a couple of photos. Typically, they'll find largemouth bass, crappies, redear sunfish and warmouths, he said.

"I said, 'All lakes need their own Loch Ness,'" Houck said.

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The two — along with Houck's son and his son's friend — found the fish in mid-November in Oak Grove Lake, Houck said. The county's parks and recreation department posted the photo to Facebook on Monday with the caption, "Anyone missing their goldfish?"

But is it really a goldfish?

Adam Cohen, ichthyology collection manager at the University of Texas' Biodiversity Center, looked at the photo of the fish and told USA TODAY he believes it's a koi. Ichthyology is the study of fish.

Cohen pointed to what he called barbels coming out of the fish's mouth.

If the fish is an adult koi, it's a relatively small one, Cohen said. Koi can grow to be up to three feet, according to the Smithsonian's National Zoo and Conservation Biology Institute.

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It's not impossible for a goldfish to grow to nine pounds, but it's unlikely, Cohen said.

"For me, looking at the photo, I can tell that's not a goldfish," Cohen said with a laugh. "It's actually a koi."

He added, "It's very common for us to see those missed IDs in our line of work. That individual actually has a standard goldfish color. Koi are extremely variable in their colors and their shape and size. That particular individual looks a lot like a typical feeder goldfish."

Houck said he received verification that the fish was in fact a goldfish, and added the fish that was found "only has fins."