Loved the little island, the water, the fisherman and the fish. Unfortunately I got bored pretty quickly which is a shame. Have you ever seen Stardew Valley's fishing mechanism? Something akin to that would spice things up a bit - either the 'progress bar' could reduce if you weren't mashing F quick enough, or you have to keep the fish in a small area of 'progress bar' which would get bigger as you level up. You could even come up with a key combination - holding one down at times to represent pulling the rod and mashing another to represent reeling in.
With regard to an 'ending' you could easily limit the game to a day - I believe anglers often buy 'day permits' for fishing here in the UK. It'd just be a case of scoring per fish and 'beat your best high score'.
Still an enjoyable little diversion though - well done.