I would like to see one or two of your underwater scenes, Greg. And this isn't done like you said. I don't think it'll work that way in TG. I had to fake it with a warped simple shape above the water (which I took out again here).
The boat, by the way, is quite small (5m), so for me the fish look quite alright. And as I said earlier, I like to check out stuff, and don't pay much attention to reality then. Just threw in some plants to make it nicer. If I were commissioned to do a reality scene, I'll certainly do that the way it should be done and do more research on relative sizes and species, etc.