Regional Specializations in the Oro-Pharyngeal Wall and Food Processing in the Carp (Cyprinus Carpio L.)

Abstract

The structure of the oro-pharyngeal wall of the bottomfeeding common carp is investigated using light-and scanning electron microscopy. Densities of taste buds, mucus, club cells and the thickness of muscular layers are measured. Distribution patterns of these elements over the oro-pharyngeal surface are reconstructed from local counts. Six areas characterized by a specific combination of morphological features are distinguished and related to twelve feeding actions composing the process of food intake and handling in the carp. These areas are the lips (detection and oral manipulation of food), the orobuccal cavity (suction and resuspension chamber of ingested food and non-food particles), the most anterior pharynx (coarse selection of large food particles), the lateral pharynx (selection of small food particles), the posterior part of the anterior pharynx (formation of boluses, transport and loading of food into the chewing cavity) and the posterior pharynx (mastication and deglutition). The conical shape of the orobuccal cavity and the slit-shaped anterior pharynx reflect two different mechanisms for particle handling viz. by suction and by muscular bulging respectively. The opercular cavities serve large volume changes for suction feeding. Protruding types of taste buds and oligovillous epithelial cells may well serve mechanoreceptive functions required for steering the process. Otherwise, specialized mechanoreceptors have not been recognized. Mucous cells producing low-viscosity sialomucines occur in the anterior part of the oro-pharynx. They will serve maintaining a laminar flow during suction and lubrication of particle handling in the pharynx. Epithelial microridges may aid in holding the mucus. High-viscosity sulfomucines only appear in the posterior part of the pharynx and will aid in trapping small particles and aggregating them into boluses. The commonly accepted alarming function of club cells and their mechanism for release is questioned in view of their abundancy in the orobuccal cavity. The structure of the muscular palatal organ is discussed with respect to its role in selection between food and non-food particles. The available information on the afferent, efferent and central neural pathways of this system is briefly reviewed. Three levels of movement, related to the particle size to be handled, are proposed. Movement of the palatal organ as a whole, local outbulging of its surface into the pharyngeal slit and a possible very local movement of the muscular papillae in its anterior part. These hypotheses are based on the almost maximal taste bud densities (820/mm 2 ) in the palatal organ, the known complex laminated cyto-architecture of the enormous vagal lobes processing its input and suggestive of a palatotopic mapping, and on the complex muscle fiber systems in this organ. The movable gill rakers of the branchial sieve, each supplied with a muscular pad and numerous taste buds (325-625/mm 2 ), suggest their additional active role in selection. Muscle fiber systems in the posterior part of the palatal as well as in the closely appressed postlingual organ serve a peristalsis-like transport to the chewing cavity. Both are copiously supplied with sulfomucines from their deep crypts. Together these morphological and physiological features allow the carp a bottom feeding behaviour requiring the effective separation of food from soiled mixtures.

Immunohistochemical study of the digestive tract ofOligosarcus hepsetus

“…The first type of mucus has low viscosity and is important to assure laminar flow during the lubrication and treatment of particles, to enable digestion to be conducted by the esophagus until the upper region of the stomach. In turn, acid GCs have high viscosity and are fundamental to trap particles [22] . The presence of these GCs was also reported in Anguilla anguilla [23] , D. dentex [21] , P. maculatus [14] , Cynoscion guatucupa (C. guatucupa) [24] , Pelteobagrus fulvidraco (P. fulvidraco) [25] and Hyphessobrycon anisitsi (H. anisitsi) [26] .…”

Response of mucous cells of the gills of traíra (Hoplias malabaricus) and jeju (Hoplerythrinus unitaeniatus) (Teleostei: Erythrinidae) to hypo- and hyper-osmotic ion stress

“…Neutral glycoproteins have low viscosity and may protect and lubricate gill epithelium against the physical injuries while the acidic and sulphated acid glycoproteins provide high viscosity and may help the adhesion of particles in suspension in water (Sibbing & Uribe, 1985) or prevent the proliferation of potentially pathogenic microorganisms in the epithelial surface (Mittal et al, 1994b). In the case of air-breathing fish, sulphated glycoproteins are also related to the protection against desiccation during emersion to take the atmospheric air (Mittal et al, 1994a;Parashar & Banerjee, 1999a, b;Chandra & Banerjee, 2003.The transference of the erythrinids, H. unitaeniatus and H. malabaricus, to deionized water (absence of ions) or water with high ion concentration resulted in changes of the chemical characteristics of glycoproteins produced by the MC.…”

Effect of starvation on the type and distribution of mucus cells in the digestive tract of the yellow drum Nibea albiflora (Richardson, 1846)

“…2). In Cyprinus carpio, the oropharyngeal cavity was found to play a major role in protection from bacterial infection and mechanical damage, in addition to serving as a buffer resisting the high acidity of the stomach (Sibbing and Uribe, 1985). Maximum number of mucus cells were found in oropharyngeal cavity which indicated the importance of this part of digestive tract.…”