THIS. It amazes me how many people think it is cruel to keep wild animals in captivity but fail to see the cruelty in releasing an animal that is not fit to survive in the wild. Sure, an injured animal can make a full physical recovery. But if that animal took a long time to recover and was in captivity for a long period of time, or if it was injured very young and spent critical periods of its development in captivity, in most cases it simply will not have the capabilities to survive in the wild. So releasing it to its death would be cruel.
Sorry for the rant. I know this has little to do with the OP. Likely the Nemo characters were supposed to be captured for the park or something like that, which totally is not ok. But I volunteer at a unique zoo where all our animals are native to the state and non-releasable for one reason or another. And it gets pretty old hearing people go on about how "cruel" we are that we don't release them.