Real River Monsters: Researcher Rediscovers Massive, 10-Foot-Long Fish

Jeremy Wade from "River Monsters" is probably thrilled. A professor has recently rediscovered a fish that lives in the swallow lakes and flooded forests in the Amazon River basin--and happens to be a massive ten feet long.

The giant fish is a species that belongs to the genus Arapaima, air-breathing giants that inhabit fresh water. For about 145 years, scientists believed that Arapaima only consisted of a single species, A. gigas. Yet the recent rediscovery of a second species proves otherwise.

So how did a researcher actually "rediscover" a fish? He apparently found it in a rare 1829 monograph. Originally named A. agassizii in 1847 by a French biologist, a catalogue published in 1868 claimed it was the same species as A. gigas. Since then, no one has questioned the ruling--until now. Donald Stewart, the researcher, found several differences between the two fish.

"In a sense, this forgotten fish has been hiding in plain sight in this old monograph, but the monograph is so rare that it now resides only in rare book collections of a few large museums," said Stewart in a press release. "I was truly surprised to discover drawings that revealed a fish very different from what we consider a typical Arapaima."

The fish described in the monograph was collected in the Amazon around 1819 and then transported to Germany as a dried skeleton. The monograph describes this skeleton and the anatomy in great detail, which is what allowed Stewart to find the differences between the two fish species. In particular, the eyes, fins and teeth of the fish were different.

Yet scientists are still unsure whether this fish still exists in the wild. The skeleton itself was destroyed when a bomb was dropped on the German museum where it was housed during World War II.

"To this day, we do not know the precise locality where the fish was collected because the German scientist who collected it died before indicating where he found it, and nobody has found a second specimen," said Stewart in a press release. "So all that exists to know the status of A. agassizii is the original drawings of its bones."

Yet Stewart remains hopeful about the fate of this species. Vast swathes of the Amazon basin have remained relatively isolated, which means that the fish could still exist. In addition, he expects the diversity of the genus to increase even further with additional studies. That should make the fans of "River Monsters" happy.

The findings are published in the journal Copeia.