Mouthpart structure and function and the feeding mechanisms ofGerres(Teleostei)

Abstract

Members of the genus Gerres feed almost exclusively on benthic invertebrates and have evolved efficient protrusible jaw mechanisms and modes of feeding. The methods employed in prey capture and feeding by five species that occur in the estuaries of Natal were studied using slow-motion cine photography and results were supplemented by field observations. All species use visual cues to detect and capture prey on or just below the surface of the substrate. The protrusible jaw mechanism is the most important feature in prey capture. Bones and muscles involved in jaw movement were studied by dissecting preserved specimens and cleaning jaws and skulls of muscle. The whole mechanism of protrusion of the mouthparts was found to be controlled by two sets of muscles acting on a modified maxilla which together with the cross-palatine ligament forms a groove along which the ascending process of the maxilla can slide when the mouthparts are protruded. The setting up of a suction pressure within the mouth further aids the uptake of items from the substrate. However, whether or not suction pressure is applied depends on the prey type.