PacFish is a 3D computer game in which players control a clownfish. The objective of the game is to collect all of the stars in each of the levels while avoiding harmful sea creatures. Set in an underwater world, the game features a rectangular grid in which underwater plants, corals, and other marine life reside. Each level is formed like a maze; players have to control the fish around the maze and collect the stars without getting caught by different creatures such as sharks, crabs, and jellyfish, among others. There are 11 different dangerous marin creatures to avoid. Some of the creatures are predictable in their movements, while some tend to follow the player around the maze. When caught by a harmful creature, the player loses a life. Players are given three lives at the start of the game.
There are 72 levels in PacFish. Players can save their game anytime. When a player loses all of the given lives, they will go back to the last saved level when the game is restarted. Players use the arrow keys to move the fish up, down, left, or right. To help players along, the game provides players with six helpful bonus items. The game also comes with powerups and rewards, including Magic Algae that turns enemy fish into delicious fish that can be eaten. Another powerup is the Turbo Boost, which makes the fish swim fast through the maze.