This is a lovely story! You definitely have that Ghibli vibe you were hoping for. I can even imagine the world as it would be in their timeless, and warm animation style, too. 
I do have to agree that there are some things a newly humanized salmon couldn’t know about the world of humans, but even with that being the case, it didn’t mess with my enjoyment of what you have written out, and available so far. The perspective of the narrative in this case can be a useful tool for describing scenery without compromising our new to humanity MC. 