This game has a nice gameplay loop! Honestly well done
My only suggestions are either;
1) Make that the minnow travel is sort of a level/wave timer so that you must survive the onslaught until the minnow crosses
or
2) If there's no more danger, make it an instant level complete instead of waiting for the minnow to cross (I am aware that there is a fast forward button and next button, but for a "final release" I wouldnt recommend to go in that route)