Preheat barbecue for high heat. Squeeze the juice from the lime wedges over fish fillets then season them with salt and pepper.
Barbecue 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 frypan over medium heat. Add the garlic; cook and stir just until fragrant, about 2 minutes. Stir in the butter, remaining lime juice and coriander. Serve fish with the coriander butter sauce.