Dang! Looks like a clean bite! A snapper could do that, but would usually finish it off. A heron would swallow the fish whole. One of the experts will chime in before long. Sounds like you need to just sit back with a rifle and see whats happening there. If a snapper is in there they usually surface periodically, and you can cut him in half. 30-06 works well. You can set hooks for them too. I'm not familiar with all the animals you Texans have that enjoy fish, but there's several guys on here from there that might have an idea.
