Difficult?
The game design itself itsn't too bad: hold to go up, release to go down. But the controls are too... slow? There really should be a way to accelerate your drop/rise, and some of the spaces between rocks/sides are really hard to get through without taking damage, because the tiniest little tingle causes Mr.Fish to grow an exoskeleton. Great attempt, keep it up!
P.S. I don't really see how the background messes with the obstacles; they are not even the same color.