Preheat a grill for high heat. Squeeze the juice from the lime wedges over fish fillets, then season them with salt and pepper.
Grill fish fillets for about 5 minutes on each side, until browned and fish can be flaked with a fork. Remove to a warm serving plate.
Heat the oil in a skillet over medium heat. Add the garlic; cook and stir just until fragrant, about 2 minutes. Stir in the butter, remaining lime juice and cilantro. Serve fish with the cilantro butter sauce.