ah, i see, (have seen a window put in a pond before now.)
well it wouln't be a good idea to put it in a dividing wall, or TBH any wall for that matter.
you can however put it in an alcove and build the wall up so it then becomes flush. BUT you still need to have access to the tank for its filtration and feeding facility.
Our not so local chinese take away has what looks like a fish tank in the wall, they cheated though, you go round the otherside of the wall and there is the tank, all they did was cut a hole in a partition wall and put the tank on a stand with some of the tank in the wall, but most on the stand, and underneath is all the filtraion gear.
which is of no use for a house becaus e the tank will be in the way