Oops! Sorry biev and mr. biev ...
I didn't make the connection to the previous thread.
In light of the facts - I have to agree with Andy M. - the less cooking surface actually touching the fish the less the chance of sticking. Heat the grill, scrub it well with a stiff brush, and oil both the grate and the fish.
Another tip is don't mess with the fish after you put it on the grill. It should not be moved until you are aread to turn it - and only turn it ONCE.