Rock Bass (Ambloplites rupestris) belong to the Sunfish family (Centrarchidae). They are native to the St. Lawrence-Great Lakes, Hudson Bay and northern Mississippi drainages, but have been widely introduced throughout the US starting in the 1800s, through the Erie Canal to the Hudson, River and to many Atlantic and inland watersheds by United States Fish Commission, the predecessor to the National Marine Fisheries Service. Rock Bass are a small (max 373 mm ) freshwater fish that are important as sport fish. hey are competitors and predators of the Redbreast Sunfish (Lepomis auritus) and the young of Smallmouth Bass (Micropterus dolomieu), trout, and other sport fish.They rarely enter brackish water, but have been found in the upper tidal region of the Connecticut, Hudson, Delaware, and Susquehanna Rivers. Further south, Rock Bass are confined to higher elevations. On the West Coast, Rock Bass were introduced in 1893 to the Chehalis estuary, Washington, where it is still established. Inroductions to the San Francisco Bay and Columbia River estuaries were unsuccessful.