Huchen are a type of fish.
Like all types of fish, each huchen gives one fish fillet when caught. The huchen is one of 4 fish that can be caught with the red lure.
Huchen can be caught with red lures in any fishing spot, but their favorite spot is #8 (the rocky area next to the fishing boat).
Huchen can be caught in large circles and therefore are easier to catch.
See Fishing List for more detailed information.
Huchen in the fishing book
The huchen is on page 8 of the fishing book:
A majestic fish that turns bright red in springtime. Likes sandy riverbeds.