Rapid voluntary stomach eversion in a free-living shark

Video observation of oral gastric eversion in a free-living Caribbean reef shark (Carcharhinus perezi) shows voluntary gastric eversion followed by retraction not only occurs, but is extremely rapid (lasting similar to 0.3 s). Eversion may occur by stomach relaxation-oesophageal contraction coupled with increased abdominal pressures to enable prolapse, and retraction by a mechanism analogous to suction feeding. This behaviour provides a 'cleansing' function for removing indigestable food particles, parasites or mucus from the stomach lining. Sharks, and possibly other animals with similar gut morphologies, may use this technique to helo maintain a healthy alimentary tract.