Happy thread-resurrection!
You say it's a "bit heavier, due to the water". Try 74KG, plus the weight of the glass!
A 40" TV is around 32" x 24". You say it's thin, so let's say 6" depth for the fishies to do a 3-point turn...
That's 81cm x 61cm x 15xm or 74,115cm cubed.
Which is 74KG just for the water.
No idea what fixings you'll need, but they will need to be pretty substantial. I like the idea of a batten as mentioned earlier in this thread, but that may be a lot of strain on the joints in the tank only being supported at the back. You may need to think about a triangulated shelf affair, stretching to the front of the tank (6" in my guesstimates).