Players are fishermen, trying to catch the most valuable fish and sell them in the market for the best prices. With limited space for storing caught fish, players must use their wits to get the right fish to market at the right times. This is where the granting of wishes is most helpful. Just catch the fish who will grant the wish you want, throw it back, and you get your wish. Sounds simple, but the game does require a bit of thinking and planning. The wishes can help you increase the value of fish when sold, grant you extra storage space, and several other useful things.
From Rio Grande Games' site.