Stringfish

The Stringfish (イトウ, Itō) is an extremely rare fish that appears in the winter (December to February), from 4 p.m. to 9 a.m.. It is caught in the river. It sells for 15,000 Bells, making it one of the most expensive fish in the game. In, the Bug and Fish window describes it as "Rarely seen and treasured, these are known for having voracious appetites."

In Wild World
Blathers will tell the player the following about the Stringfish upon its donation to the Museum:

"I've heard it said that this fish is actually very high in fat content... If such words are true, then whatever possessed someone to name it that? If you were to call a portly fellow "stringy", well... Madness would ensue!"

The Stringfish can then be seen swimming about in the first freshwater tank.

In City Folk
After donating the Stringfish, Blathers will impart his knowledge of the fish to the player:

"...Stringfish are hardy creatures that can live for up to 15 year with ease! These older fish grow to remarkable sizes actually... One fish even made it to a gargantuan 80 inches (2 meters)! At that size, perhaps we should call it the king of the river! No wonder it looks so serene, eh wot?"

The Stringfish can be found in the middle-left tank in the aquarium.

Fishing Tourney
Chip will not eat this fish as an entry for the Fishing Tourney. He will mention that it is too special to eat as it is. He will accept it as an entry and will measure it as usual.

In New Leaf
The following information will be displayed by its tank:

"Stringfish live in cold rivers, can grow to over a yard long, and are stout and bulky like logs. They live up to 20 years but grow so slowly that it takes them 15 years to reach full maturity. They are called "phantom fish" because there are so few of them. Adults are particularly hard to find."

The Stringfish can be found in the larger of the two left-hand tanks in the freshwater fish room.

In New Horizons
"The stringfish grows slowly, but also lives quite a long time for a fish, with up to 15 years being typical. Consequently, while it takes a while, they can get quite large-perhaps even up to six feet long! The stringfish is perhaps the best embodiment in the fish world of 'slow and steady wins the race' "

The Stringfish can be found in the middle waterfall tank in the freshwater fish room.

Further information
The Hucho perryi is one of the largest, most ancient type of salmon species which inhabits the lower to middle reaches of lakes and rivers. It is Critically Endangered. Females lay between 2,000 - 10,000 eggs each time on sandy/gravelly river bottoms, most of them do not hatch. The fish can be found in areas of the Northwest Pacific, namely the Sakhalin Island (Russia, where it gets the name Sakhalin taimen), the Island of Hokkaidō (Japan) and parts of the far eastern Russian mainland.