Interesting idea!
I didn't quite get why shrimp - but I totally loved the shrimp movement animation :) Although death from lighting is a bit weird, especially at first - it's counter-intuitive that the shrimp gets shoved off the building when it gets a lighting hit :) Also the enemies are a bit too hard to manage - I never managed to get one killed while it was grabbing me. Maybe they should be introduced a bit later, when you have at least a few towers?
That said - great submission, and a quite unique game mechanic!