Cooking a whole 30lb sturgeon on a spit
Based on my experience as a chef I wouldn't recommend spit-roasting your sturgeon. It's a rather large fish for that technique although smaller fish may work. Your idea to wrap it in wire albeit a good idea, give a moment to consider what would the wire do to your fish as it cooks. Proteins shrink when they cook and although  you may wrap the fish in wire while it is still uncooked the wire will not shrink to accommodate the shrinkage of the fish.A 30 lb. sturgeon would probably be roasted and there will be less complications when it comes serving it whole (given you have a big oven!)