Remove the pin bones from the fish and set on a rimmed baking sheet or platter.

Drizzle the olive oil over the fish and season with salt and pepper.  Turn the fish over in the oil and seasoning until well coated on both sides.  With the skin side down, drizzle the lemon, lime and orange juice over the fish.  Cover the fish with the onion and citrus slices.  Season again with salt and pepper and set aside for 10 minutes.

Preheat the grill to medium-high.

Place the fish on the grill skin side down, reduce the heat to medium, and close the grill.  Cook for 10 minutes.  Using a long metal spatula, carefully turn the fish 180 degrees.  Use tongs to pick up any citrus slices and onion that may have fallen off of the fish and place them back on top.  Close the grill and continue to cook 10 minutes longer, or until the fish is opaque and just cooked through.   Remove from the grill then set on a cutting board or serving platter.

To serve, cut the fish into pieces with a knife or serve the fillet whole, family style, allowing guests to scoop the flesh from its skin onto their plates with a large serving spoon.