I enjoyed the art, game play loop was simple, but solid. Visual damage cues would be nice, but still pretty recognizable . As much as I love the intro building up to show all the fish on the main menu, I'd love a "retry" button to jump back in immediately.
I loved the wavy background effect of the water, super slick.
Neat that this was emulated for GBA. I've played with GB studio, but didn't know there was a GBA engine out there!
Good work!