Japanese Giant Fish, Part 5- River Monsters

Posted by: mystery_man on July 3rd, 2010

Japanese rivers have long been the haunts of mysterious giant creatures. Here let us examine a couple of the more well known such enigmas.

Tone River “Grayback”

The Tone River, located in the Kanto region of Honshu, is the second longest river in Japan, at 322km (200 miles) long.

The Tone River

In recent years, this river has had several reports of mysterious large fish said to be over 2 meters (6.6 ft) in length. Accounts tend to mention a large, slow moving fish of some kind that is known to float leisurely up to the surface and lazily sink back down again.

A particularly harrowing report came from a fisherman who was out fishing for bass on his boat. The fisherman reported that a huge fish with an oversized head appeared out of the depths and circled slowly around his boat for some time. The man reported the fish as being 3 meters (10 ft) long, a size he was able to confidently estimate since the fish was as large as his own boat. The eyewitness said that on several occasions the colossal fish came so close to the boat that he began to fear that it might actually be capsized by the beast.

Another account comes from a group of people who observed a giant fish casually swimming along for several minutes from one of the many bridges that span the river. The fish eventually slowly sank down out of sight as the surprised onlookers watched in amazement. It did not resurface.

Most reports of this mystery fish describe the back of the creature as being a dark gray in color, leading it to be nicknamed the “grayback.”

It has been speculated that the culprit is likely a giant carp or catfish of some kind. Many large species of carp can be found in the river, including the grass carp (Ctenopharyngodon idella) and the black carp (Mylopharyngodon piceus), introduced species from China that can reach huge sizes. Interestingly, the black carp typically has a sort of dark grey coloration on its back.

black carp

giant catfish

There has even been speculation that the creature may be some sort of wayward shark that travelled inland, a pinniped, or even a lost baby whale.

Let us look at yet another mysterious river dweller.

Edo River’s “Eddie”

Another Japanese river that has had its share of giant fish stories is the Edo River, allegedly home to a 2 meter (6.6 feet) long fish that has been affectionately nicknamed “Eddie” by the locals.

The Edo River

The fish has startled many fishermen along the river’s shores and one man even claims to have once had the monster on his line before it broke off and escaped.

Speculation as to what the creature could be has ranged from a giant catfish or carp to some sort of large fish that has made its way inland from the sea. Carp of several species are plentiful throughout the river.

Interestingly, during the 70s the Edo River was the location of a series of bizarre sightings of a strange, seal-like creature that was said to mewl like a cat, and has come to be known as the Matsudodon (named after nearby Matsudo City). Could the eyewitness accounts of Eddie be of a similar creature and are they possibly the result of people seeing a pinniped of some type that has travelled from the ocean?

Northern fur seals (Callorhinus ursinus) are known to inhabit northern Japanese waters. Although this species is not known to typically be found so far south, a wayward specimen could have feasibly made it’s way up the Edo river.

Out of place seals have been documented in Japanese rivers before. In 2002, a bearded seal (Erignathus barbatus) was sighted in Tokyo’s Tama River and subsequently went on to become a sort of celebrity, even garnering the nickname “Tama Chan.” The seal went on to frequent other rivers throughout the area. Bearded seals dwell in the arctic, and like the northern fur seal, typically inhabit only the most northern of Japanese waters. They are not known to be found as far south as Tokyo.


Could a wayward, out of place pinniped also be behind sightings of this mysterious river monster?

An offshoot of the Tone River, the Edo River is also located in the Kanto region of Honshu. The 59.5 km (37 mile) long river flows into Tokyo Bay.

About mystery_man

One Response to “Japanese Giant Fish, Part 5- River Monsters”

  1. springheeledjack responds:

    Okay, for the fishermen who’ve come across these things, I’m making an assumption here based on what you’ve said, but would it be safe to say that the fishermen are convinced that these mystery fish are in fact something else not usually seen.

    Where I’m going with this is I am ASSuming the fishermen are very familiar with catfish and carp…even larger specimens…so the fact that they are reporting these large fish sightings without any sort of identification tagged to them leads me to believe they are seeing something non-indigenous to the rivers. Again, I’m ASSuming the fishermen have seen enough carp and catfish to recognize the heads, backs and tails of such animals so that they would be able to make a reasonable identification if it was just a carp or a catfish.

    If so, then that leads me to believe that what is being seen is either some new species or something that has been coming up the rivers from the sea. As we’ve seen, there are sharks that can convert from salt to fresh water. And ten foot long isn’t especially large sized for a shark.

    Again, I would defer to the fishermen who spend their lives on the water and have probably seen more fish than all of us put together over the years.

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