In our world, human species have been preserving fish by drying since Homo heidelbergensis, and salt curing for at least 60,000 years. But somehow a world that has domesticated animals, ocean-going vessels, elaborate fabrics, wheels and axles and multi-story architecture didn't figure out the most basic food preservation?
This kind of weirdness puts a damper on an otherwise excellent story.
This is one of the manga that is/has gone heavy on the "we explain Stuff to kids" tack.
And is going about it like the blind leading the lame...
And never forget... For the majority of people reading this, Food Comes From the Supermarket, or from a Deli/Restaurant/FastFood Franchise.
In Big City Japan, home of the Almighty Vending machine, probably even more so.
And let's be fair.. Properly drying/smoking fish to preserve it has a couple of tricks to it that you do need to know to prevent severely reducing the life expectancy of you or others by eating it.
As with any form of food preparation, the principle is really simple, but proper execution is crucial and less trivial.