How do you barbeque a whole piece of fish?
I BBQ whole fish or fish filets with or without skin quite regularly. You suspect the BBQ was too hot, but usually BBQs are not hot enough (unless you were REALLY hot and over like 800F?). Make sure grill is clean and apply oil to the grill and to the fish. Put fish skin side down on the BBQ until crispy and flip fish until cook to your desired temp. It might stick a bit, but it should not stick so much that it causes problems.

Common problems might be:


Sticky grill because it is dirty and not oiled
Grill is not hot enough
Fish is flipped too soon and did not get a chance to cook enough to separate itself from the grill
Fish is flipped more than once
Fish surface is not oiled (I suggest also oiling the flesh side)
Using a thick spatula (thin metal is better)
Pushing spatula hard to get under the fish. You don't need to do this. Just slide the spatula slowly under the fish if you find it is a bit sticky and more progressively.
A dirty BBQ or applying to much oil could perhaps cause a flare up. You can usually listen for the flames and if you hear fire or see it then use a spray bottle with water to disrupt the flame.