Place Cusk in a shallow baking dish and season with salt and pepper. Whisk together garlic, rosemary, oil and lime juice in a small bowl. Pour 3/4 mixture over Cusk, toss and marinate 15 to 30 minutes.
Preheat grill to a medium-high heat. Place Cusk on grill, and cook 4 or 5 minutes on each side, or until the fish flakes easily with a fork. Remove fish and Drizzle some of the remaining marinade over the finished product.