The Arena is where you can train and battle your fish. There are certain amount of fish you can use for the Arena. They are labeled "Arena" in the store. The way the fighting works is like rolling dice, when u get a higher number "win" will appear next to the area you won in, "Lose" will appear in the area where the the number you have is lower than your opponents you must have two or more area u won in or you will lose. The type of fish also depends on how well your fish perform.