Pectoral Spine Locking and Sound Production in the Channel Catfish Ictalurus punctatus

Abstract

We examined the anatomical basis for locking and sound production of the pectoral spine in the channel catfish, Ictalurus punctatus. We separate two related phenomena, binding and locking, both of which previously have been termed locking. Binding of the spine can occur in various partially abducted positions by applying muscular force to actively engage two friction-locking mechanisms. The spine's dorsal process presses against the spinal groove of the cleithrum laterally, and its anterior process presses against a bony apron on the scapulocoracoid medially. Locking occurs when the spine is fully abducted and requires no additional muscular force. In this position, forward motion is prevented because the posterior end of the anterior process presses against an internal excavation in the lateral wall of the scapulocoracoid. Posterior motion is prevented by a catch that holds the anterior edge of the anterior process against the side of the elevated apron. The spine is unlocked by posterodorsally torquing the spine around its long axis, thereby lifting the edge of the anterior process above the imprisioning apron. Stridulation sounds are produced during spine abduction when ridges on the ventrolateral surface of the spine's dorsal process contact the ventrolateral wall of the cleithrum's spinal fossa. These sounds contain groups of pulses that vary in frequency, amplitude, duration, and pulse patterns. Individual pulses are generated by successive contacts of these ridges with the wall of the spinal fossa. The pulse frequency spectrum appears to be determined predominantly by the pectoral girdle, a nonspecialized acoustic radiator, and the swimbladder does not play an active role in sound production.