Why Does the Fish Dish Disappear after Being Enchanted?
The sushi chef is that good of a chef that he can improve the quality of fish by not doing much else to it but magic or something. Your fish are disappearing because you used the fish to enhance itself, because the only thing you need to enhance a fish is multiple of the same fish. The first enhancement requires 3 of the same type of fish, then it increases to like 6 or whatever it was, to 10, etc.
You have to make sure that you have enough fish (or don’t need that fish for dinner service) before choosing to enhance it. If not, then you’ll just need to catch those fish again the next day to sell it for the improved price.
And, yes, the sushi restaurant will only serve so many customers per day so if you overload the menu with more food than is needed, any unsold fish is basically trashed. You can’t retrieve it once you assign it to a menu slot or afterwards when the dinner service is over, so try to keep count of how many dinner items you are adding and how much is actually selling. 30+ sushi items when you’re still just a silver rated restaurant, for example, is way too much, I found.
The sushi chef is very particular and only uses fresh fish that hadn’t been left sitting in the kitchen for too long during that dinner service. Ironically, you can add fish that you’ve let sit in your inventory for over a week without much issue but I suppose he doesn’t truly know what you caught during that day or what might have been caught three days ago.
I think the damned cat that you see sitting on the counter in the mornings probably eats whatever isn’t sold.