Do you mean by closed, they will not sell any?
Closed as in recycle systems not attached to outdoor waters.
I was just looking and most of them seem to be Aquaponics facilities.
Tilapia are legal in MI. Have been for quite some time. At least 12-13 years since I have been occasionally checking in on what the heck the State is up to.
Here is an approved species list for Michigan:
Approved Species Michigan 
