That's the message that Peta wants to put across.
"The largest tank in the world cannot come close to the vast oceans and lakes that are the natural homes of these animals," said a spokeswoman for the group.
Peta also pointed out the responsibilities that come with keeping a fish.
"Our fear is that the fish will be left to suffer when people grow tired of feeding them and cleaning the aquariums."
Finding Nemo became the biggest animated film of all time in the US after it was released there in the summer.