TIC-TAC-TOE : GAME :: trout : fish
The best answer is fish. The relationship between the first pair of words, TIC-TAC-TOE and GAME, is that of item to category—one word names something that fits into falls into the category, or group, named by the other word. Therefore, the second pair of words must also have an item-to-category relationship. A trout is a type of fish.