Due to the high density of water, sound travels 4.8 times faster and over longer distances under water than in air. Consequently, sound production via stridulation is an excellent means of underwater communication for channel catfish. The pectoral spine of the channel catfish is an enlarged fin ray with a slightly modified base that forms a complex articulation with several bones of the pectoral girdle. Unlike the other pectoral fin rays, the individual fin segments of the spine are hypertrophied and fused, except for at the distal tip. The surface of the spine is often ornamented with a serrated edge and venomous tissues, designed to deter predators. Sounds produced during fin abduction result from the movement of the base of the pectoral spine across the pectoral girdle channel. Each sweep of sound consists of a number of discrete pulses created by the ridges lining the base of the pectoral spine as they pass over the rough surface of the girdle's channel. The stridulation sounds are extremely variable due to the range and flexibility of motion in fin use. Different sounds may be used for different functions in communication, such as in behavior towards predators and in asserting dominance.