For your Finding Nemo party theme, here is a game idea that can be altered to fit the Finding Nemo party theme.
Check out Finding Nemo
Party Games for more free party games. Finding Nemo is an underwater adventure between a father and son, Nemo, a boy clownfish, who is tragically stolen away from the safety of his coral reef home, and his timid father must search the dangerous and unforgiving ocean to find him.
CENTIPEDES: Divide the players into 2 teams of 10-20 members each. The teams form up in the file. Each team is given a rope. The players take the rope with their left or right hands from the both sides evenly. Then each player takes him/herself by the right or left ankle. At the leader's command the centipedes jump 10-12 m forward, holding the rope with their hands. Then they turn around and jump backward. The players may also run with the both feet, but in this case the players must stand in the line closer to each other. The team which manages to jump or to run to finish line the first becomes the winner (while running the players mustn't let the rope off).