The goldfish is very cute indeed! A very nicely polished entry! :)
I got as far as the green (grassy) levels before getting frustrated and giving up. I struggled a bit with controlling the character's horizontal movement precisely so succeeding often felt more like luck than skill. Tapping the controls for fine adjustments didn't seem to do much. Maybe you used physics based movement, so the friction prevents movement until you get some momentum?
The gravity inversion mechanic reminded me of a game called VVVVVV from 2010: