First, let me say that I'm rooting for this fish. I'll be anxious for more photo/video evidence of his recovery.
Second, I think some people need to take a step back and put this in perspective. No comparison between the fish owner suffering a serious injury/receiving treatment and this $5 oscar's situation need be made. It's a fish that has a couple seconds of memory and whose entire internal structure works differently than ours in a situation like this. It's not a human being. We lose a leg, they stop the bleeding and give us an artificial leg. Nobody is gonna give this fish a new tail, but there is nothing wrong with giving it a chance to survive on it's own.
This is not a gold fish, it's memory is longer than a couple seconds.... I agree that if it's not suffering and has a chance of survival, it should not be killed, but don't use false information to support your argument

