Overall, a very relaxing game.
I like the graphics, the only thing I would alter is the button and inventory background - it doesn't really match the aesthetics for me.
One thing I found a little frustrating is, that for the first 8 casts the fish always got away. Surely this is not intended, maybe a bias for actually catching towards the beginning of the game might be good, to keep players encouraged to play, as they had that initial accomplishment.