Would fish you rehydrated over such a long time even be safe? I've never heard of desalting something without refrigeration that took more than, like, overnight.
Yeah it's pretty weird that they put the dried fish in water that long. We just boil it when making a curry. Though some people do keep them in water if it's too salty but only for about an hour.
Also no way dried fish would taste similar to fresh fish even after rehydration(at least not for fish and chips). From googling I think the mangaka was talking about salted fish not dried fish.