If I had a 14-inch datnoid, or a 14-inch anything, in a 40-gallon tank...I would not only expect it to be stressed and uninterested in food, but I'd be fasting it as much as possible in an effort to maintain water quality (such as it is...). I get that the fish is not being kept that way by choice, but that doesn't change the fact that you need to do something about a bigger tank sooner rather than later.
As Winston Churchill said, it's not enough to do your best; you simply must do what needs to be done.