Cool concept, but poor execution and lots of glitches/issues:
When you get too big, your shields stop working. It creates a smaller shield that you don't actually fit into and it never disappears, but it doesn't protect you anymore.
As you get bigger it becomes impossible to squeeze through bigger fish without shields, which, as I mentioned before, stop working.
You should have more than one life if the mines equal instant death. So annoying.
The area should get bigger or deeper as you get bigger.