Food handling in the carp (Cyprinus carpio): its movement patterns, mechanisms and limitations

Abstract

The oropharyngeal feeding mechanism of the carp was analysed as a case study for cyprinids. Light and X‐ray cinematography combined with electromyography allowed a detailed analysis of the external and internal events during processing of the following food types: radtopaque pellets, earthworms, barley, tubificids, cladoceran suspensions and food‐soil mixtures. Ten patterns of head movements serve 12 feeding actions: paniculate feeding and gulping for intake; rinsing, repositioning, selective retention and spitting for selection; gathering from the branchial sieve, transport, loading of the teeth, crushing, grinding and deglutition. Muscular cushions in the pharyngeal roof (palatal organ) and floor (postlingual organ) permit postcapture selection between food and non‐food and transport. Protrusion of the upper jaw is crucial in food processing and serves different aims in particulate intake, gulping and internal selection.The mechanism of each single pattern and its effects in manipulating the flow and particles is discussed. Restrictions for processing different types of food are formulated. Tentative limits are set to the feeding on the available food types in the environment. The feeding apparatus appears to be unsuitable for exploiting very small particles (< 250 μm), plant and other materials of fibrous content. Only slow and immobile food particles with a diameter up to c. 4% of the carp's body length are effectively processed. The carp appears to be a generalist in its diet, with specializations for the exploitation of food and non‐food mixtures from the bottom, even if the contained food is of considerable density and hardness.The distinct elements of feeding behaviour are considered to be stereotyped action patterns. They are released and steered according to the actual size, distribution, consistency and contamination of the food and integrated into varied probing and feeding sequences. Different food types require different movement patterns and ‘handling times’. Protrusion with closed mouth appears to be a core pattern in food handling as it is basic to several feeding actions (repositioning and back‐washing during purification; gathering of retained food from the branchial sieve).Protrusion and the palatal and postlingual organs in this lower teleost are basic to the substrate feeding habits of many cyprinoids and are discussed in relation to (i) the hypertrophy of the pharyngeal masticatory apparatus, (ii) the recruitment of body power for mastication, and (iii) the evolutionary loss of toothed upper pharyngeal transporting bones. A scheme connects the unique character set of cypriniform fish to the origin and evolution of their feeding mechanism.The cooperation between functional morphology, ethology and ecology for the study of niche separation between species is emphasized.