From the Super Mario Wiki
The Fishing Barrel is one of the Barrels owned by Funky Kong in the Game Boy Advance remake of Donkey Kong Country. It is located in his establishment, Funky's Flights (renamed to "Funky's Fishing" in this version) along with the Jumbo Barrel. The fishing barrel transports Donkey Kong and Diddy Kong to the coast of Donkey Kong Island to play the world's Funky's Fishing challenge. The game's manual even reads "Jump into this barrel to be transported to the open seas."
The Fishing Barrel resembles a Bonus Barrel, except it has a fishing hook on its side rather than a "B".