Sticklebacks are spiny-rayed fishes in which the spines are separated from one another and each has its own separate fin membrane. The caudal peduncle is slenderer than in other Great Lakes fishes and the pelvic fins are each reduced to a single stout spine with rudiments of one or two soft-rays. Many forms occur in northern seas and fresh waters along the Arctic shores and on both sides of the North Atlantic and North Pacific. The threespine and ninespine sticklebacks are shore inhabitants in the larger Great Lakes. The brook stickleback lives in streams and bog ponds, especially where other fish species are sparse. The three-spine stickleback is famous for its elaborate courtship and nesting behavior. In the spring the male stickleback constructs an elaborate tunnel-nest of vegetation. Fewer than 100 eggs are usually laid and these are vigorously guarded by the male.