"Fish don't make bubbles because they breathe water" They don't. They breathe air. They just filter it from the water. ;)))) I know that's what you meant, I'm being daft, but not long ago I worked in a nuclear installation where they had huge ponds with radiactive flasks at the bottom. The water in those ponds is de-oxygenated so if you stick a fish in, it'll drown. Nothing floats in them, either, and if you were daft enough to try and swim in them (!!!!) you'd sink straight to the bottom.