You wanna ‘keep’ a Dory-fish?
Preserve their habitat, so your grandkids can see Dory-fish too.
Please please PLEASE don’t buy any blue tangs, clown fish, or any other fish/invertebrates in these movies. If you really want to see these pretty fish, there are many established aquariums which house some local and tropical fishes in well kept homes.
Also saying this because there is apparently a sea otter in the movie, but DO NOT APPROACH SEA OTTERS. They might look cute, but they are CRITICALLY ENDANGERED, and disturbing it can potentially cause it to waste precious energy fleeing from you; energy it needs to grow, maintain body heat, forage, and what not. It is also ILLEGAL in the United States to harass a marine mammal.
If you really love the animals in this movie, protect them and their homes.