In a thick bottom pan, heat butter with olive oil. Add diced onion and cook until onions are translucent. Add garlic and keep stirring, garlic cooks very quickly so make sure that it does not burn.
Add arborio rice, and warm stock. Keep adding the stock gradually and let it reduce until you achieve a creamy texture.
Add cooked crab and more stock, let it reduce again.
Add prawns, lemon zest and lemon juice and a little bit of stock. Let it reduce.
Add parmesan cheese, and a piece of butter and stir them in.
In a pan, add some sea salt and olive oil.
Add sea bream skin down and add a tiny bit of olive oil.
Cook on both sides for a few minutes until it's cooked through.
Divide risotto between bowls or plates, top with sea bream and serve immediately.