Neat little game, well done. I like the pixel art and I absolutely love the choice of game engine to learn a new language! :)
I’ve seen some fish spawn directly on the scene, and one even learned how to fly (see screenshot). :D
It felt like the longer the line was becoming, the slower the pace of the gameplay. It would perhaps be great to add more mechanics with the upgrades so the player is more occupied while descending the line.