This zone is found below the lower limits aquatic plant beds, h is cold, dark and has a silty-bottom. The sucker feeds on detritus and may forge at night moving into shallow waters. The Razorback sucker has adapted for life in large moving rivers. The back rises steeply behind the head which forms an inverted keel, water flows against this keel pushing the fish against the bottom. This allows the fish to feed and move in the swift water.
Some species have a terminal mouth and resemble some cyprinids.
While a few cyprinids have a subterminal mouth that resembles suckers. The main difference between suckers and cyprinids are the number of teeth and shape of the pharyngeal teeth. Suckers usually have ten or more comb-like pharyngeal teeth, one row on each pharyngeal arch. Food is ingested and broke up by the pharyngeal teeth, then digested in a long winding intestine. The Cyprinids are in the family Cyrinidae and include carps and minnows.