I think I now understand what you are asking. Is it morally right for a human to toy with an animal? Is catch and release just an acceptable and legalized version of kids throwing rocks at a dog?
To address your question, or what I think is your question, I have to ask another. Are you different than a fish? That is a stupid question on the surface, but what I really mean is do you believe that you are an animal, no different than a bear, or an elephant, or a dog? Or do you believe that you are something different, something higher, something created with a divine spark?
If we are just another animal, separated from our wild cousins only by opposable thumbs and the fact that we are not afraid of vacuum cleaners, then the answer is simple. Ethics are man-made and are determined by societies. There are no ethics in the wild. Animals do what animals do, without a moral dilemna. Personalities differ, actions differ, reasons differ, but none are immoral. Cats play with mice. Killer whales smack seals around, and wolves eat elk while they are still alive. You may choose to release a fish out of pity's sake, or so you can catch it or its offspring again later, or because you don't want to carry it with you. If we are just animals, then morality is based solely on law. So if what you are doing is legal, it is moral. The reason behind the action is irrelevant, it is the action that determines its morality.
But if you believe we are something different, that we were created separate from the animal kingdom, that our bodies are no more than vessels for our eternal souls, then the reason for your action is far more important than the action itself. Are you fishing because you enjoy tormenting fish, or because you are awed by the natural world, and have a desire to experience it first-hand? Law doesn't determine morality, one's own sense of right and wrong determines morality. In this option there are legal immoral actions, and moral illegal actions.
For my own part, I think God created trout so that we could truly appreciate streams. And I don't think that the fish hold it against us.
Life is hard. But it's a lot harder if you're stupid.