Catfish's Maw is the fifth dungeon in The Legend of Zelda: Link's Awakening. It is located inside a giant stone catfish in Martha's Bay, which may have sparked inspiration for the similar Inside Jabu-Jabu's Belly from The Legend of Zelda: Ocarina of Time. The dungeon offers the Hookshot and, after defeating Slime Eel, the Wind Marimba.
Catfish's Maw is the fifth dungeon that Link explores in order to collect the eight Instruments of the Sirens hidden across Koholint Island. All eight are needed to awaken the Wind Fish from his slumber atop Mt. Tamaranch, thus allowing Link to return home to Hyrule. Link is able to enter this dungeon after obtaining the Flippers from the Angler's Tunnel, the fourth dungeon.
Inside the dungeon Link defeats Master Stalfos in a duel only to discover that the skeletal warrior has stolen the vital contents of a treasure chest from an adjacent room, leaving only a taunting message behind. Link pursues Master Stalfos around the dungeon, battling him twice more before Master Stalfos realizes that he cannot outlast Link. Deciding to fight to the death, Master Stalfos is defeated on the fourth encounter, leaving behind the Hookshot that he had taken from the chest.
With the Hookshot in hand, Link proceeds to the boss, Slime Eel. The eel immediately recognizes Link as "the outsssider, come to wake the Wind Fisssh...", and pledges to eat him. Link slays him with the Hookshot. As he dies, Slime Eel mocks Link's foolishness, claiming that Link does not know 'what kind of island' Koholint is—referring to the fact that the island will disappear once the Wind Fish is roused. Apparently unperturbed, Link claims the fifth instrument, the Wind Marimba, and leaves the dungeon.
Use of the Hookshot enables Link to access the sixth dungeon on his quest, the Face Shrine.
Catfish's Maw is located in the exact center of Martha's Bay in the southeast corner of Koholint Island. Because it is surrounded by water on all sides, Link cannot access the catfish's 'square' of the island until he has obtained the Flippers from the previous dungeon, the Angler's Tunnel, however, this also means that he can obtain the Wind Marimba before the Surf Harp.
Most of the dungeon is below the water level, but the fish statue's head protrudes above the surface of the lake, allowing entry via its mouth (or 'maw', hence the name). The head is surrounded by a wall of rocks, and anyone wishing to enter must first dive underneath them. The only point where Link can pass under the stone ring is in the small 'bay' created by the formation of the rocks to the west of the catfish. By diving here, Link passes under the barrier and emerges in front of the gaping cavern.
Unusually, this level contains two opponents which could conceivably be called the mini-boss. The first was Master Stalfos, a particularly large Stalfos armed with a sword and shield. Link defeats Master Stalfos once, only to have him escape with the Hookshot. After three more clashes, Link finally destroys Master Stalfos and reclaims the Hookshot.
The second mini-boss is a pair of Gohma, which guard a door en route to the boss. These spider-like enemies can be handled one at a time, so their numbers do not make the fight significantly more difficult.
The final boss of Catfish's Maw is the Slime Eel. Five holes are found within the boss' chamber, from which the Slime Eel sticks its tail through one hole and its head through another during the battle.